While the Boston Celtics added an All-Star this offseason in veteran big man Al Horford, the team will likely need help from some of its younger players if it hopes to make a noticeable leap and truly challenge the Cleveland Cavaliers in the Eastern Conference.

For Day 5 of our Celtics Summer Forecast, we asked our panel: Which young player on Boston’s roster will have the biggest impact on the team this season? Respondents were given five choices of players with one year’s experience or less: Jaylen Brown, Terry Rozier, R.J. Hunter, Jordan Mickey and Demetrius Jackson.

Brown and Rozier each landed on 10 (47.6 percent) of the ballots cast by our 21-member panel, and Mickey earned a single vote (4.8 percent).

That Brown and Rozier led the pack shouldn’t come as much of a surprise. The departure of Evan Turner leaves an obvious need for both a wing and a ball handler off the bench. Celtics coach Brad Stevens leaned heavy on Turner’s Swiss Army knife-like versatility, and Turner’s impact on last season’s team was reflected in him finishing fifth in the voting for the league’s Sixth Man of the Year.

Which young Celtics player will most distinguish himself this season? This writer’s vote leans toward Rozier because of Boston’s need for ballhandling. Brown, the No. 3 pick in this year’s draft, is going to get minutes, in part because the Celtics are thin on small forwards behind Jae Crowder (though both Gerald Green and Jonas Jerebko can play there, and Marcus Smart can defend the position).

Rozier, the No. 16 pick in the 2015 draft, simply looks as if he’s ready to compete for a role, especially after playing with poise and confidence in summer league. After being thrust into playoff minutes when Avery Bradley was injured in the first-round series against the Atlanta Hawks last season, Rozier should be more prepared to make an impact out of the gates this season. If he can run the second-unit offense and showcase his speed and athleticism — as well as those springy hops that helped him consistently rebound when he was on the floor — there’s an opportunity for him to impact this year’s team.

Brown might acclimate quickly, but it will be interesting to see if he gets a lot of those whistles that went his way while attacking the basket in summer league. Rookies don’t typically get a lot of calls. Brown’s defense could help him stay on the court and his draft position suggests he’ll eventually be a key part of this team, but it’s rare that 19-year-old rookies kick down the door right away.

Some thoughts from our panel:

Jay King, MassLive (Rozier): After losing Turner, the Celtics badly need another offensive creator. Though some of those reps should go to Smart, Rozier roasted the summer league competition and stated his case for a regular rotation role. Brown should also get minutes, but he’ll need to figure out how to harness his physical tools.

Ryan Bernardoni, CelticsHub (Brown): Rozier probably will be the best player from the group, but Brown plays a position with less depth and more flexibility. Even with the addition of Green, I think Brown will have the most impact. As a rookie, we’ll see if that impact is positive or negative.

Ben Mark, Red’s Army (Mickey): I’m going to be a contrarian here. Rozier is coming off a strong summer-league showing and Brown will get plenty of chances as the No. 3 pick, but there’s an opportunity for Mickey to make a consistent impact as the fourth big on the roster. If Mickey can provide high energy and rim protection against opposing second units and finish around the rim, it’s going to be hard not to play him. He oozed potential in his limited minutes last season.

Sam Sheehan, Celtics Reddit and CLNS Radio (Rozier): For me, this question came down to Rozier and Brown. Brown’s chess-playing Twitter avatar is fantastic, but I ended up going with Rozier. Even though a free-throw-filled summer league went a long way toward comforting me, I’m still not totally sold on Brown being a big-time, day-one contributor because rookies rarely are. I think Smart’s role will expand in the absence of Turner this season, and people will realize just how much Smart was being relied on to play well outside of his regular position. That said, I think Rozier will absorb the remaining minutes for a team that desperately needs shooting and could use rebounding help from its guard positions. The Celtics’ biggest hole is still the backup small forward position behind Crowder, and though Green was signed as a stopgap, it’s easy to see Brown sliding into that role and earning minutes. I think the second-year player (Rozier) is going to be more ready than the rookie (Brown), and we’re going to see Rozier build on a strong summer league and become a regular part of the rotation.

Sean Penney, CelticsBlog (Brown): When you get drafted as a high lottery pick, you better be able to make an impact. Also working in his favor is that the Celtics don’t have as much depth on the wing. Boston is loaded with guards, leaving few minutes available for Rozier or Hunter.

Jeff Clark, CelticsBlog (Rozier): I think Rozier is ready to make a big leap this season. He’ll get minutes off the bench, and I think he’ll pick up a lot of the responsibilities Turner handled last season. Brown has the most talent and has the opportunity to slide into a backup wing position behind Crowder, so he’s next on my ballot.

Alex Kungu, CelticsBlog (Brown): I’m in the minority probably, but after watching Smart play at small forward last season, the need for another wing was a lot bigger than some might realize. Brown might not have the biggest impact in terms of scoring, but he’ll defend, create a little bit and get himself to the line. He’ll be someone who consistently plays beyond the box score.

Wes Howard, CelticsBlog (Brown): Brown slightly edges out Rozier here, mostly because of available minutes. There just aren’t enough players on the team who can consistently play the 3. Brown will take over Turner’s creating/slashing responsibilities and should improve — particularly defensively — as the season goes on.

Jon Duke, Celtics Stuff Live on CLNS Radio (Rozier): Rozier made a leap in last season’s playoffs and we saw in summer league that progress has continued. Rozier is yet another example of what confidence does for a player’s game. The unsure Rozier we saw in 2015 summer league was unproductive and lost, but the Rozier we saw last month might have been the best player in the entire summer league. My only question about Rozier is where he’ll get his minutes. Small-ball lineups will help, but with Isaiah Thomas, Bradley and Smart in front of him, it would take injuries or a trade for Rozier to truly make the impact he’s capable of.

Justin Poulin, Celtics Stuff Live on CLNS Radio (Brown): I’m going to say Brown because I’m a fanboy and because of depth and opportunity. He’ll get regular minutes for certain, even if they are limited. I would love to go with Rozier here, but he’s not the best bet barring injury or trade. You can’t predict either, so we’re going with what we see through green goggles.

Mike Dynon, Red’s Army (Rozier): If Brown earns enough playing time, he’ll be in position to win this category. However, the better bet right now is Rozier. A dominant summer league is a prerequisite to making an impact when the games are real, and Rozier has raised the bar for himself. Last season, he was content to crash the boards from the backcourt, hand the ball off and not look for his shot. But if he continues with his newfound aggressiveness, he could become a difference-maker.

Jake Keaney, CelticsBlog (Rozier): While it is only summer league, Rozier’s performances in Utah and Vegas were impressive. He looked more confident in his ability to score and handle the ball, and it would be worthwhile to give him a chance to fill Turner’s role of backup facilitator. Given that he’s still on a rookie-scale contract, I think it makes more sense to at least try Rozier out in that role before splurging on a veteran name and potentially harming Rozier’s development.

Sam Packard, WEEI.com (Brown): My brain says Rozier. My heart says Brown. My brain’s heart also says Brown.

Bill Sy, CelticsBlog(Rozier): Without Turner, Stevens will look to Smart and Rozier to handle the ball more for the second-unit offense. Rozier showed this summer that he has developed as a playmaker and is ready for a larger role. He’s not the probing point guard Turner was, but he has learned to change speeds and that has made his quick-burst attack more effective off the dribble. He showed off his inside/outside game by shooting 45 percent behind the 3-point arc and getting to the line 49 times in six summer games. He’ll pair nicely with Amir Johnson in the pick-and-roll, with Jerebko and Brown attacking from the wings.

Jared Weiss, CLNS Radio (Brown): Although Rozier looks better prepared for the regular season, he is still stuck behind Smart at the third guard spot. Brown will be competing with Hunter and Green for minutes off the bench as a wing, so he is likely to see at least 20 minutes per game. Stevens used the wing position a little different last season, as Turner served as a primary ball handler in bench lineups next to Smart. But this season expect lineups using Smart as the point, with Rozier and Brown playing the wing around him. Brown will get ample opportunity to find transition buckets and backdoor cuts with that tenacious defense.

John Karalis, Red’s Army (Rozier): Rozier had a very nice summer, displaying a bump in his decision-making and ability to exploit bad defenses. We’ll see how it translates to the regular season, but he made the first-to-second-year jump you really like to see. I’m excited to see what Brown becomes, but the Celtics have the luxury of bringing him along slowly, so I won’t expect much from him this season.

Dan Greenberg, Barstool Sports (Rozier): It has to be the darling of summer league in Rozier. The step forward he showed in both Utah and Vegas has Celtics fans giddy with excitement. He looked much more in control and showed elite flashes with an ability to get to the rim. Even his jump shot looked much improved. The minutes will be there for Rozier, and I don’t see why he wouldn’t capitalize on them.

Mark Van Deusen, CelticsLife(Brown): This is a two-man race between Rozier and Brown. The question is, which one will get more time on the floor? Both players’ 2016-17 stock probably fell a bit with the Green signing. As great as Rozier was last month in Utah and Las Vegas, it was still just summer league. He did earn Stevens’ confidence in last year’s postseason, so Rozier will probably get more burn than Brown out of the gate. However, by the end of the season I like the No. 3 pick’s chances to have the greater impact of the two.

Rich Jensen, Red’s Army (Rozier): You know I really wanted to say Brown, but I think it’s going to be Rozier. Rozier is going to get more minutes than Brown and looks to be much farther along in the “giving the game what it needs” department.