Golden State's Butler out for season with ACL injury: agent
Butler, 36, was helped off the court after falling following a collision with the Miami Heat's Davion Mitchell during Golden State's 135-112 win over his former team on Monday.
Butler's agent Bernie Lee said in a statement to ESPN on Tuesday that an MRI scan had confirmed a season-ending torn anterior cruciate ligament.
"Obviously a gut punch on every level for Jimmy and the entire group, but I firmly believe that this is a part of the journey," Lee told ESPN.
"We can't only expect to take the good things out of it. I've known for over 10 years now that Jimmy is going to win a championship before he is done. My belief in that is unwavering."
The Warriors have not yet confirmed the diagnosis for the six-time NBA All Star.
"We're all really concerned but we'll know more after the MRI obviously. We don't know anything at this point," Golden State coach Steve Kerr said on Monday.
"Everybody is subdued because of the injury waiting to hear the news."
Butler has averaged 20.1 points a game in his first full season at Golden State since joining from Miami last year.
Butler's injury comes with the Warriors enjoying a mid-season resurgence which has seen them move up to eighth place in the Western Conference standings.
Lee meanwhile backed Butler to return from the injury stronger than ever.
"If you know anything about Jimmy, you know exactly how he will attack this challenge," Lee told ESPN. "Put simply, he has this."