Atlanta starting center Clint Capela suffered a hyperextended right knee in the first half of the Hawks' 107-101 play-in game win over the host Cleveland Cavaliers on Friday night and did not return.
There's initial optimism that Capela didn't suffer significant damage to the knee, but an MRI on Saturday will determine the extent of the injury, sources told ESPN's Adrian Wojnarowski.
Speaking after the game, coach Nate McMillan said Capela is sore but noted the team won't have an update on his status until Saturday.
The injury occurred late in the first half when Cavaliers center Evan Mobley fell against Capela's leg as Mobley was falling down, after which the Hawks center also fell to the court and clutched his right knee in pain.
Capela's teammates quickly surrounded him, and he had to be helped off the court just before halftime, at which point the Cavaliers led 61-51.
The 27-year-old Capela entered the game averaging 11.1 points and a team-high 11.9 rebounds.
The Hawks advanced to face the Heat, the top-seeded team in the Eastern Conference, in a first-round playoff series that begins Sunday in Miami.