Jimmy Butler was taken from the court on a stretcher/wheelchair combination as the Chicago Bulls lost on the road to the Denver Nuggets.
The two-time All-Star posted 18 points and five rebounds in an impressive first-half before falling hard after a Joffrey Lauvergne foul.
Butler picked himself up to sink one of two free throws and ensure he wasn't ruled out of the game but called for immediate medical assistance. He was unable to return to action as the Bulls fell 115-110.
The 26-year-old sprained his left knee in an awkward fall and will have an MRI scan today. Bulls beat writer Vincent Goodwill tweeted he will sit Saturday's game in Minnesota but could return either Monday or Wednesday.
Despite the injury, Butler was in high spirits at the Pepsi Center; Nick Friedell reported the 2015 Most Improved Player joked with medical staff as he limped into the Bulls locker room.
Butler has been the standout player for the 27-22 Bulls and holds career-high averages in points (22.4ppg) and assists (4.3apg).
The Chicago franchise has gone 3-6 in their past nine games to drop down the Eastern Conference. Eight back from leaders the Cleveland Cavaliers, the Bulls will be sweating on the fitness of their main man.