The "good Rex, bad Rex" debate returns to Chicago.
Bears quarterback Kyle Orton was taken from the field on a cart late in the second quarter Sunday, and a source told ESPN's Michael Smith that a high ankle sprain will sideline him at least a month.
Orton will have an MRI on Monday, the source told ESPN.
Orton got up and took a few steps, then crumbled to the ground. He was tended to for several minutes before being carried off. He was 8-of-14 passing for 108 yards.
The Bears also lost safety Mike Brown to a calf problem late in the first half.
Grossman threw for a touchdown and ran for another as the Bears outscored the Lions 14-0 in the second half. He had lost the starting job to Orton in training camp after an uneven 2007 campaign.
"I always thought odds are I was going to play a little bit, so we'll see what happens," Grossman said.
Information from The Associated Press was used in this report.