The top pick in the 2006 draft, Bargnani had not played since tearing a ligament in his right elbow in a Dec. 10 loss at Portland. The 7-footer also injured his right wrist in that game when he fell awkwardly on a dunk attempt.
Bargnani had started in every appearance for Toronto since Dec. 29, 2008, when he came off the bench in a loss at Golden State.
Toronto's Aaron Gray, who has had double-digit rebounds in four straight games, started at center against the Celtics.
The Raptors went 13-13 without Bargnani, who is averaging 16.0 points and 4.3 rebounds in 21 games.