Rondo, who wore a bulky brace that immobilized the arm in case of contact, scored eight points and had five assists in 26 minutes of Boston's 98-90 overtime loss.
"He looked OK this morning [at shootaround]," Celtics coach Doc Rivers said before the game. "We just gotta wait and see. It's very similar to [Shaquille O'Neal], you have to look with your eyes and make a decision. It's the same with Rondo. I think he'll be OK though, I really do.
"He still has legs and he still has speed. He's just gotta play the game with the same force that he played the other night and that's for the whole team. Rondo's force and ball pressure, that's very, very important for us. So that's what we'll be watching. If he can't do that, if he can't play with speed, then he's not going to be very effective."
Celtics backup guard Delonte West, who bruised his left shoulder during the second quarter of Saturday's win, also played. He scored six points in 13 minutes.
"Delonte's fine," said Rivers before the game. "He's hurting, obviously, the shoulder is bothering him. But he looked fine [at shootaround]."
To be safe, the Celtics activated veteran Carlos Arroyo to add depth at the point guard position in case either Rondo or West was limited. Boston's healthy scratches were Avery Bradley, Troy Murphy, and Sasha Pavlovic.
Rivers also said that O'Neal responded well to his first activity in more than a month after playing 8½ minutes in Game 3. Rivers wants to see more of what O'Neal provided in his brief second-half stint.
"The first half, I thought [he labored]," said Rivers. "But I thought in the second half, he was really good. He gave us exactly what he could give us and what we needed. I don't know if there's a breakthrough for him. You get on the floor the first time and you're tentative. I thought he was far more aggressive in the second half. We need more of that."
Before Monday's game, Heat president Pat Riley gave a handful of individual pep talks to his players on the Garden floor after the team's morning shootaround. Rivers, who played under Riley with the New York Knicks, said those words could go a long way.
"He's a hell of a speaker, I guarantee that," said Rivers. "There's no better speaker that I've been around in my life. So I guarantee you that, whatever he said, reached them. And they'll play with amazing intensity."
The Heat lead the Eastern Conference semifinal 3-1.
Chris Forsberg covers the Celtics for ESPNBoston.com.