Butler suffered the injury while pivoting in the lane after an offensive rebound.
He fell to the ground holding his knee and was subsequently helped off the court.
Butler, one of the most talented players in the league, averages 22.4 points per contest.
Butler, acquired from the Bulls during the offseason, is one of the biggest reasons the Wolves entered Friday 11 games over.500 and in fourth place in the Western Conference standings.
While no information on Butler's condition was not given immediately, the Olympic star seemed to give himself a self-diagnosis to his teammates while being carried off the floor.
He's averaged 37.7 minutes per game over the last five seasons, which leads the National Basketball Association.
Butler came down with a rebound late in the third quarter, and after taking a hard dribble, collapsed in pain.
From a fantasy perspective, if Butler is out for the rest of the season, look for guys like Nemanja Bjelica, Jamal Crawford and Andrew Wiggins to benefit in terms of playing time.