Coach Greg Vanney said Thursday that an MRI shows the 33-year-old midfielder has a Grade 2 sprain of the medial collateral ligament.
"Timeline-wise it's weeks, it's not months," Vanney told reporters Thursday. "We'll see just how he progresses, I guess. He'll be out for a little while."
Bradley was injured during stoppage time on a foul by Impact midfielder Emanuel Maciel, whose red card on the play was downgraded to a yellow after a video review.
Bradley has started seven games this season. He has 12 goals and 29 assists in 200 career MLS games (199 starts) with Toronto (2014-20) and the MetroStars (2004-05).