The Bulls own a 2-0 lead over Eastern Conference top seed Boston in their best-of-seven opening round playoff series ahead of game three Friday night at Chicago.
Rondo suffered the injury Tuesday in Chicago's 111-97 victory at Boston, with an exam and x-rays showing a fractured thumb.
Surgery will not be required to repair the injury, but no timetable for his return was given.
"It's tough when any of your soldiers go down, especially somebody who plays as hard as he does and loves the game so much," Bulls guard Jimmy Butler said.
In the game-two triumph, Rondo had 11 points, a team playoff record-tying 14 assists, nine rebounds and five steals. With another rebound, he would have had the Bulls' first playoff triple-double since Scottie Pippen in 1997 during Chicago's glory days with Michael Jordan sparking six titles.
Rondo has averaged 11.5 points, 10.0 assists and 8.5 rebounds a game for the Bulls as they try to go from a 41-41 season and the worst record in the playoffs to a shock upset of the Celtics in round one.
"We're all right. We're still expecting to win," Butler said. "No one is here moping around. That's what you have to do. You can't sit around feeling bad because he's gone."
When Rondo is in the game, the Bulls are outscoring foes by 14.6 points, but when he is not on the court, the Bulls are being outscored by 5.4 points.