Joe Mazzulla talked to the media after the Boston Celtics overwhelmed the Cleveland Cavaliers 138-107 on Sunday. Despite the dominating win, a reporter brought up an issue Boston has struggled with in the preseason. The Celtics failed to secure as many rebounds as they could have.When asked for the solution to that issue, Mazzulla responded (via Noa Dalzell):“Find five guys that will rebound.”In the win against the Cavaliers, the Celtics had 39 defensive rebounds. On paper, that certainly looks impressive after averaging 33.9 on that end last season. However, the Celtics gave up 21 on the offensive glass, almost half of Cleveland’s 43 total rebounds. The Cavs starters, led by Larry Nance Jr.’s five, combined for 13 offensive rebounds, one more than the Celtics as a team.Joe Mazzulla’s Boston Celtics also faced the same issue against the Toronto Raptors on Friday. Toronto hauled 34 rebounds, 15 coming from the offensive end. Boston had 35 defensive rebounds alone, but could not secure as many possessions as the game presented.Last season, the Cs allowed just 10.7 offensive rebounds, ninth best in the NBA. In three preseason games, they are giving up 16.3, a figure that would have been at the bottom of that statistic last season by a wide margin.Joe Mazzulla’s best centers last season are no longer with Boston CelticsJoe Mazzulla’s most reliable big men over the past few seasons are no longer with the Boston Celtics. The team traded Kristaps Porzingis to the Atlanta Hawks and lost Al Horford (Warriors) and Luke Kornet (Spurs) in free agency.The three averaged 18.3 rpg, a significant loss for the Celtics. What does not show on the stat sheet are the size, length and willingness to battle under the boards to prevent opponents from grabbing offensive rebounds.Jayson Tatum, last season’s team-leading rebounder with 8.7 rpg, is recovering from an injury, potentially compounding Boston’s rebounding problems.Without the Kornet-Horford-Porzingis rotation, Mazzulla will lean on the unproven Neemias Queta, Luka Garza, Xavier Tillman and Chris Boucher. The preseason is not a true regular-season performance indicator. Still, Joe Mazzulla made it clear what his frontliners must do to solve the Boston Celtics’ preseason rebounding problems.