With Lauri Markkanen out, Nikola Mirotic gets first start for Bulls since Bobby Portis fight

Chicago Bulls rookie Lauri Markkanenwas ruled out of the team's game Monday night against theBoston Celticsdue to back spasms.

The 7-footer had started all 25 games this season and is averaging 14.7 points and 8.1 rebounds.

Bulls coach Fred Hoiberg didn't sound very concerned that this would be a lingering issue for Markkanen.

"He had one episode [of back spasms] in the summer when he was playing with his [Finnish] National team," said Hoiberg. "He got over that very quickly. He had the issue in preseason, he also got over that very quickly.

"He had treatment this morning after shootaround; he said it was a little bit tight and it just tightened up a little bit more throughout the course of the day. So he'll get another round of treatments tonight, another one tomorrow before practice, and hopefully we'll get him back real soon."

Replacing Markkanen in the Bulls' starting lineup wasNikola Mirotic, making his first start of the season.

Mirotic missed Chicago's first 23 games after suffering a concussion and facial fracture in a fight with teammate Bobby Portis.

ESPN's Nick Friedell contributed to this report.