Jimmy Butler's return from knee strain undetermined

— -- MINNEAPOLIS -- An MRI on  Bulls All-Star swingman Jimmy Butler revealed a left knee strain, the team said Saturday, and there's no current timetable for his return. 

"Right now, it's a strain," coach Fred Hoiberg said before tipoff. "He's actually on an airplane right now heading back to Chicago. He'll see our doctors in the morning, and we should get a better idea about time frame and see what we want to do for treatments."

The Bulls had already ruled Butler out for Saturday night's game against the Minnesota Timberwolves. Hoiberg said Butler won't play Monday at Charlotte, either. Hoiberg did not rule out the possibility of Butler playing in the All-Star Game next weekend in Toronto. 

"Obviously, Jimmy does a lot for us on both ends," Bulls guard Kirk Hinrich said. "We've kind of rode him at times this year when we've had injuries, and now he's down. So other guys are going to have to step up, and we'll have to take the challenge."

Butler was hurt late in the second quarter of Friday night's loss to Denver, when he went up for a basket and was fouled by Nuggets big man Joffrey Lauvergne. Initially, it appeared as if Butler's right knee got caught underneath him as he fell, but it was the left knee that he injured. 

Butler stayed in the game to take his free throws before being carted back to the locker room for evaluation. He walked out of the training room about 15 minutes later and was wearing a large ice pack around his left knee. 

"He said he heard something pop," Bulls point guard Derrick Rose said. "But with my knees, I knew that it was something serious. But I came back [to the locker room] a couple of times when I was using the restroom -- it just seemed that they were icing it, and I guess it was nothing major."

Saturday marked the second game Butler has missed this season. The 26-year-old sat out Wednesday's matchup against the Kings because of left knee tendinitis. 

In other injury news, Pau Gasol, who missed Friday's game with a left hand injury, was set to return against the Timberwolves. 

Veteran Mike Dunleavy, who has not played all season after back surgery, was set make his season debut. He was expected to have a minutes restriction.