Giannis Antetokounmpo says being without Khris Middleton for any length of time would be a "tremendous loss" for the Milwaukee Bucks.

Middleton sprained the medial collateral ligament in his left knee during the fourth quarter of the Bucks' 114-110 loss to the Chicago Bulls on Wednesday.

Head coach Mike Budenholzer confirmed Middleton will undergo an MRI scan on Thursday to determine his status for the rest of the first-round playoff series, which is level at 1-1.

At the very least, the 30-year-old faces a race against time to be ready for Game 3 on Friday, and Antetokounmpo acknowledged that would be a huge blow for his side.

"We need this guy. When he asks for a sub, you know that it's bothering him because he doesn't leave the game," Antetokounmpo said.

"You expect him to get up and walk it off and get back to the game, but you see he was limping and limping and you're thinking like, 'Oh, I hope it's not bad, I hope it's not bad."

Middleton had scored 18 points and provided eight assists before leaving the game and has averaged 20.1 points, 5.4 rebounds and 5.4 assists this season.

He averaged at least 21.5 points in the past four playoff series and had 24 points, 6.3 rebounds and 5.3 assists per game in the NBA Finals.

"We have a job to do here," Antetokounmpo added. "Khris is one of the best players on the team, if he's not able to be with us, it's going to be a tremendous loss for us."

Antetokounmpo led the scoring for the Bucks with 33 points, but that was not enough as the Bulls – inspired by 41-point DeMar DeRozan – levelled up the series.

The Bucks also lost Bobby Portis in the first quarter after being caught in the face by an elbow from Tristan Thompson, but Budenholzer is optimistic he can make a swift return.

"We anticipate he should be fine with some time and that he should be good," Budenholzer said.

DeRozan's career playoff-high scoring return ensured the Bulls beat the third-seeded Bucks for just a second time in 19 meetings.

"No matter what you did in the regular season, this is a brand new start and new mindset," DeRozan said. 

"You could see it in all the guys. It doesn't matter if we'd lost 20 times to those guys. This is an opportunity for us to compete. We've got to take advantage of it."