Caruso was fighting through a screen set by Giannis Antetokounmpo when Carter's elbow hit him on the nose with 1:44 remaining in the second quarter. Caruso fell to the floor and was bleeding from his nose before coming out of the game.
The Bulls were examining Caruso for a potential concussion, which makes his status for Game 5 on Wednesday unclear, according to coach Billy Donovan. The Bulls trail the series 3-1 with Game 5 set for Wednesday in Milwaukee.
"I think there was enough there that they had some concerns that it was [a concussion]," Donovan said after the game. "To the level, I'm not really sure. He'll obviously go through all the normal protocols and questioning and things they normally go through."
Caruso did not score but contributed four assists, four rebounds, a steal and two blocks in 17 minutes.
In his absence, Bulls rookie Ayo Dosunmu came into the game and started the second half. Dosunmu played 29 minutes and finished with eight points, but the Bulls' reserves have failed to provide much production all series.
They were outscored by Bucks guard Grayson Allen alone on Sunday, 27-17.
Earlier this season, Caruso fractured his left wrist after a flagrant foul from Allen during a Jan. 21 game against the Bucks. The injury would sideline him for two months.
Carter was ruled for an offensive foul on the play, and Donovan did not believe there was any malicious intent on the play.
"It wasn't really necessarily a flagrant play at all," Donovan said. "[Caruso] just got caught up in a screen there going for the ball and he got hit pretty good. It was right in front of our bench. He was trying to come back in, but once he started bleeding they wanted to bring him back and get the bleeding to stop. And then, I think, once they started looking into him, there was enough of a concern that maybe he has a concussion."