Amir Johnson is also expected to join the starting lineup, alongside the usual collection of Avery Bradley, Jae Crowder and Al Horford. This would put Gerald Green on the bench after the forward started seven games this postseason.
The Celtics go on the road Sunday to take on the Cleveland Cavaliers down 0-2 in the Eastern Conference Finals.
Smart had a strong third season in the NBA while averaging a career-high 10.6 points per game. Unfortunately, he has struggled this series with just 10 total points scored in 46 minutes across two games.
He was 0-of-6 from the field in Game 2 while finishing minus-24 on the court.
Johnson has been in and out of the starting lineup throughout the postseason, although he hasn't been very effective regardless of where he begins the game. He played just five minutes and scored zero points after starting Game 1 of the series, then scored two points in 12 minutes off the bench in Game 2.
The Celtics will need both players to step up after declaring Thomas out for the rest of the year due to a hip injury. The All-Star averaged 28.9 PPG during the regular season and was a major reason the squad reached this point in the postseason.