Lowry practiced Saturday morning, with Raptors coach Nick Nurse saying Lowry "looked OK."
Game 1 between Toronto and Boston will be at 1 p.m. ET (ESPN).
Lowry turned his ankle in the closing game of Toronto's first-round series against the Brooklyn Nets on Aug. 23. He was dribbling up the court in the first quarter when he was cut off and stepped on the foot of Nets guard Chris Chiozza.
After limping to the sideline during a timeout, Lowry re-entered the game but immediately felt more pain. He limped through one possession and then committed a foul while signaling to the bench that he needed to exit.
While the Raptors went 12-2 without Lowry during the season, they would like to have him at full strength for their conference semifinals matchup against the Celtics.
The Celtics are the only team to defeat Toronto in Orlando since the NBA resumed play in the bubble -- a 122-100 victory over the Raptors on Aug. 7.