Portis and Mirotic were involved in a "serious altercation" at practice on Tuesday that eventually sent the latter to the hospital.
Both parties were aggressive leading up to the conflict, according to Bulls vice president John Paxson, but Portis threw the punch that ultimately landed him with his suspension. He's a competitive kid, but in this instance he made a mistake.
The Bulls announced Wednesday that Mirotic suffered maxillary fractures and a concussion and will likely undergo surgery. K.C. Johnson of the Chicago Tribune reported that Mirotic may miss a few weeks over the incident. He's one of four healthy Bulls big men. Rookie Lauri Markkanen will probably draw the start at power forward against the Raptors on Thursday night, Robin Lopez will start at center and Christiano Felicio will stay plenty busy as basically the only backup big on the Bulls' roster for the moment.More news: Xbox One's Fall Update is Here with Home Personalisation and New Features
Mirotic, 26, averaged 10.6 points and 5.5 rebounds in 70 games last season and was expected to have a starting role for the Bulls this season after inking a two-year deal worth $12.5 million with Chicago.
Portis, 22, was battling for backup minutes.
Joe Cowley of the Chicago Sun-Times reports that animosity between Portis and Mirotic had been building for years and that the two forwards had gotten into a "handful" of shouting and shoving matches in practice since the 2015-16 season.