Boozer is out after suffering an ankle sprain Wednesday against the Charlotte Bobcats. Deng was in the lineup despite a left thigh bruise that made him a game-time decision against the Hawks.
"[Boozer is] better today, but still, he won't be able to go [Friday]," Thibodeau said before the game. "But a lot better today ... It's just going to be day to day and athletic trainer Fred [Tedeschi] told me that it's better, but he's still got a ways to go."
Boozer fell hard after taking a hit by Kwame Brown, who was called for a flagrant foul on the play. X-rays proved negative and an MRI on his sprained left ankle did not reveal any damage.
"We lose a pretty important piece," Joakim Noah said before the game Friday. "But I think that we're a team that's dealt with adversity all year. And this is a big game so we're excited for the challenge."
Boozer missed the first 15 games of the season after breaking his right pinkie on Oct. 2. He is averaging 18.3 points and 9.6 rebounds in his first season with the Bulls.
Kurt Thomas started in Boozer's place.
Deng averages 17.4 points and 5.8 rebounds in a team-high 39.1 minutes a game. After missing 64 games the past three seasons, Deng and Keith Bogans are the only Bulls to start all 64 games this season.
The Bulls (45-18) have won 11 of 13 and trail Eastern Conference leader Boston by 1½ games.
Nick Friedell covers the Bulls for ESPNChicago.com and ESPN 1000.