MILWAUKEE -- Bucks forward Khris Middleton sprained the medial collateral ligament in his left knee during the fourth quarter of Milwaukee's 114-110 loss to the Chicago Bulls on Wednesday, coach Mike Budenholzer said after the game.

Middleton is scheduled to undergo an MRI on Thursday, which will determine the severity of the injury and give the team more information about a timeline for his return.

Middleton slipped on a drive to the basket about midway through the fourth quarter in Game 2 of this first-round series, completing a pass to Brook Lopez as he fell to the ground. Middleton immediately began favoring his left leg, attempting to stretch and flex his leg on the sidelines before he headed to the locker room.

Middleton finished with 18 points, 8 assists and 5 rebounds in 33 minutes for the Bucks.

"You expect him to get up and walk it off and get back to the game, but you see that he was limping and limping and limping and you're thinking like, 'Oh, I hope it's not bad, I hope it's not bad,'" Bucks star Giannis Antetokounmpo said after the game. "We need this guy. When he asks for a sub, you know that it's bothering him because he doesn't leave the game."

Over the past two seasons, the Bucks are 86-34 (.717) when Antetokounmpo, Middleton and Jrue Holiday are all on the floor together, including the playoffs. However, Milwaukee did outscore opponents by 7.8 points per 100 possessions when Antetokounmpo and Holiday played without Middleton on the floor.

"We have a job to do here," said Antetokounmpo, who finished with 33 points and 18 rebounds. "Obviously 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."

The Bucks had already lost another key member of their rotation, Bobby Portis, earlier in Game 2. He exited in the first quarter after getting hit in the face by an elbow from Bulls center Tristan Thompson while the two went up for a rebound.

No foul was called, but Portis fell to the ground after contact and was bleeding near his right eye after the play. A pool report with crew chief Kane Fitzgerald said the officials did not see the elbow during the play.

Portis attempted to warm up briefly after halftime but stayed on the court for only a short period of time before heading back to the locker room. Shortly after the third quarter began, the Bucks ruled him out for the rest of the game with a right eye abrasion.

Portis scored two points and grabbed two rebounds in six minutes.

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

The injury news wasn't much better prior to Game 2 for the defending NBA champions. Budenholzer said during his pregame media availability that veteran guard George Hill wasn't expected to return anytime soon from the abdominal strain that has prevented him from playing in the series.

"We don't expect him in the short term," Budenholzer said.

Budenholzer said this issue is unrelated to the neck injury that caused Hill to miss 17 games earlier in the season. Hill said after returning from that injury that he'd been dealing with a partial tear between the sixth and seventh thoracic vertebra in his spine.

According to Budenholzer, the latest injury stems from something that happened in the Bucks' April 8 game at Detroit. Hill hasn't played since.

"We'll see how he progresses over the next I'd say handful of days or more," Budenholzer said.

Hill, 35, played 54 games during the regular season and averaged 6.2 points, 2.9 rebounds, 2.2 assists and 23.2 minutes.

Jevon Carter filled Hill's spot in the rotation the Bucks' 93-86 Game 1 victory and scored three points in 10 minutes. He contributed two rebounds in nine minutes Wednesday.

The Associated Press contributed to this report.