The team said he is out indefinitely.
"It's just one of those situations that literally breaks your heart,'' Suns coach Monty Williams said. "Dario is a guy that I've been with twice. I coached him in Philly, and to get a chance to be with him here, he's what Suns basketball is about. Hard worker, unbelievable guy and he was so looking forward to playing in these Finals.
"And to play a few minutes and have that kind of injury, it was a tough thing to hear this morning.''
He checked out of the game with 1:43 remaining in the quarter and had to be helped off the court to the Suns' locker room, finishing with one rebound and one missed shot in two minutes of play.
The five-year veteran came into the Finals averaging 4.8 points and 2.6 rebounds in 11.1 minutes per game during the Suns' postseason run.
Craig has been a regular part of the playing rotation, but Kaminsky hasn't seen much time in the postseason.
"We have different options," Williams said. "Frank gives us quality size and playmaking ability. He's smart. We went small last night with Torrey. We also have Doolie [Abdel Nader], who can play some small ball ... So we're just going to try to make those decisions on the fly. But those three guys come to mind."
ESPN's Dave McMenamin and The Associated Press contributed to this report.