Chicago Bulls forward Nikola Mirotic suffered a fractured jaw and a concussion after fighting with teammate Bobby Portis in practice, the NBA reported on its website on Tuesday.
The Bulls said Mirotic would likely require surgery and they were considering disciplinary action over the incident.
Mirotic, 26, was set to start when the Bulls open their season on Thursday in Toronto. He averaged 10.6 points and 5.5 rebounds last season before re-signing with the Bulls on a two-year, $27 million deal just before training camp.
Portis, also a forward, averaged 6.8 points for Chicago last season.