WASHINGTON, Oct. 18 -- The Chicago Bulls Wednesday suspended forward Bobby Portis for eight games for punching teammate Nikola Mirotic during an altercation that left Mirotic with facial fractures and a concussion.

Mirotic is expected to miss at least four to six weeks.

John Paxson, the Bulls' vice president of basketball operations, acknowledged that both players' tempers escalated during practice Tuesday.

"Both players owned responsibility in the incident itself," Paxson said Wednesday. "But only one player threw a punch. And that punch is inexcusable. It's not who we are. It disappoints us in terms of what happened, and because of that we're going to suspend Bobby for eight games."

The incident is a blow to a Bulls franchise in the midst of a rebuild. Mirotic was expected to start in coach Fred Hoiberg's revamped lineup, having beaten out Portis. Now, rookie Lauri Markkanen will get his first career start during the season opener Thursday against the Toronto Raptors.

"Bobby Portis is not a bad person," Paxson said. "He's a good kid. He's a competitive kid, but in this instance he made a mistake. And as we all know when you make mistakes you got to suffer the consequences."

Mirotic and Portis have spent two full seasons competing against one another for playing time.