The Celtics had an unquestionably successful season. They earned the No. 1 seed in the Eastern Conference, made the conference finals, and Isaiah Thomas earned an All-NBA selection. However, they realized they are still one step away from competing for a title after their loss to the Cavaliers.

Cleveland quickly disposed of Boston in five games and a large part of that was due to frontcourt play. Kevin Love and Tristan Thompson caused problems for Boston during the entirety of the series, whether it was rim protection, rebounding, or just being a force inside. The Cavs' interior was better than Boston's in every way. Which is why the Celtics are prepared to make some serious upgrades.

"Multiple league sources have told CSNNE.com in recent weeks that the Celtics are focused on landing an All-Star caliber talent in the frontcourt.
 
That makes sense when you consider how guard-dominant the Celtics were this season and how that had a negative impact on the team's rebounding and, to a lesser degree, their defense as a whole."

Via CSNNE 

Boston's current frontcourt is Al Horford, Kelly Olynyk, Amir Johnson, and Jonas Jerebko. They will ocassionally move Jae Crowder up to play as a small ball four. That's a solid group of players talent wise, but they lack the size, rebounding, and rim protection necessary to take on bigger lineups like Cleveland.

Unfortunately for Boston, the upcoming free agency period doesn't feature too many frontcourt players that fill their needs. Players such as Paul Millsap, Serge Ibaka and Blake Griffin are available but all three come with different weaknesses. There will be no magic fix for Boston. At least not this summer.