Butler suffered the injury in the third quarter of the Timberwolves' 120-102 loss to the Houston Rockets at the Toyota Center in Houston.
The four-time All-Star missed a layup and ripped down his own rebound. When he landed on the floor, Rockets big man Nene appeared to land on his right leg. Butler twisted away from the contact, but when he went to plant his right foot, his leg gave out. He went down hard onto the floor. Butler grabbed at his right knee.
His teammates helped him off of the floor and he did not return to the game. Butler scored 10 points and had five rebounds and three assists in 25 minutes for the Timberwolves. The 28-year-old shooting guard leads the NBA with 37.3 minutes played per game.
Timberwolves coach Tom Thibodeau announced after the game that Butler will undergo an MRI on his knee on Saturday. Sources told Yahoo Sports that X-rays on Butler's knee returned negative on Friday night.
Butler leads the Timberwolves in points per game, field goal attempts, steals and minutes played. The Timberwolves host the Chicago Bulls at 9 p.m. Saturday at the Target Center in Minneapolis.