"He took a pretty bad fall, got bent up. He has a midfoot sprain, and it's pretty tender and sore right now," Celtics head coach Ime Udoka told reporters Monday. "We'll get him round-the-clock treatment, and right now he'll be listed as questionable."
Smart appeared to suffer the foot injury when he fell over Milwaukee Bucks superstar Giannis Antetokounmpo during the Celtics' 109-81 win in Sunday's Game 7 of the Eastern Conference semifinals.
The 28-year-old Smart, who was named NBA Defensive Player of the Year for the 2021-22 season last month, averaged 14 points, 5.7 assists and 3.5 rebounds against the Bucks in the East semis. He missed Game 2 of that series due to a right quad contusion.
Celtics center Robert Williams III, meanwhile, didn't suit up in the Celtics' decisive victory over the Bucks on Sunday. Udoka said before the game that Williams was available, but he didn't want to disrupt the team's rotation.
Udoka said Monday that Williams will have zero restrictions entering the series against the Heat, noting that it will be easier to reintegrate him at the beginning of a series.
"Rob is available, just like he was [Sunday] night," Udoka said. "I mentioned he'd be on a needed basis, and he's available, no minutes restriction.
"I'm always going to be a little bit cautious with guys coming off a layoff without touching the court, but it's a little bit different starting a new series as opposed to being injected into a Game 7 or Game 6, or whatever the case was before. But he's available, looking better every day, and getting more confident in that."
For the Heat, star point guard Kyle Lowry was ruled out for Tuesday night's Game 1 against the Celtics. He will miss the contest due to a lingering hamstring injury that has kept him out of multiple games this postseason.
Lowry only played in three games during the Heat's first-round series against the Toronto Raptors. He appeared in just two games during Miami's second-round series against the Philadelphia 76ers.
The 36-year-old Lowry has averaged only 6.2 points and 5.2 assists this postseason. He last suited up May 8 against the 76ers in Game 4 of that series, compiling six points, seven assists and three rebounds in the loss.
In addition to Lowry, the Heat listed Max Strus (hamstring), P.J. Tucker (calf), Caleb Martin (ankle) and Gabe Vincent (hamstring) as questionable for Game 1.