CHICAGO -- Rajon Rondo is out indefinitely with a broken right thumb, just when everything seemed to be going well for the Chicago Bulls.

The team announced the injury on Friday, hours before the Bulls host the Boston Celtics in Game 3 of their first-round playoff series. Chicago won the first two games in Boston and is trying to become just the sixth No. 8 seed to knock off a No. 1. Being without the veteran guard certainly doesn't help.

"Rondo obviously has been unbelievable in the two wins we had in Boston," coach Fred Hoiberg said. "So to get the news we got last night obviously was very difficult."

Hoiberg said Rondo was injured swiping for the ball in the third quarter of Game 2. He either hit the ball or Boston centre Kelly Olynyk's elbow, but stayed in the game. He was a limited participant in practice on Thursday.

X-rays confirmed the fracture, and surgery is not required. Hoiberg said Rondo -- also playing through a right wrist injury -- will probably be re-evaluated in a week to 10 days.

Hoiberg said it's "too early to tell" if Rondo would play in the second round should the Bulls advance. Without him, Jerian Grant starts with Michael Carter-Williams backing him up. Jimmy Butler and Dwyane Wade also figure to run the offence at times.

"It's tough when any of your soldiers go down, man," Butler said. "Especially someone who wants to win as bad as he does, that studies the game and wants to do well by everybody like he does. It's definitely a loss for all of us. But damn. I mean, we wish we had him, but we don't. There's not too much more to say about it."

Rondo's play in this series is a big reason why the Bulls are threatening to become the first eighth seed to sweep a top seed.

He played well in Game 1 and was particularly good in Game 2, just missing a triple-double with 11 points, 14 assists and nine rebounds as the Bulls put Boston in an 0-2 hole. Just as important was his defence on Celtics star Isaiah Thomas, which took some of the load off Butler.

The injury comes at the end of an up-and-down first season in Chicago for Rondo. A four-time All-Star who won an NBA championship with Boston in 2008, he was at the centre of a major flare-up in January. He fired back at Butler and Wade while defending the team's younger players after the two stars criticized the team following a loss, resulting in fines for the veterans.

Rondo also got suspended for a game by the team earlier in the year and was in and out of the rotation. The Bulls sat him for five straight games at one point, but he started down the regular-season stretch and played well.

"Rajon's experience in these types of settings is invaluable," Hoiberg said. "To miss that now with him being out, most likely for the rest of the series, it does put some extra responsibility on some guys. Again, we've been through this. We had other guys that have had to step up in players' absences."