Amir Johnson missed Thursday's exhibition against Real Madrid, Adam Himmelsbach of the Boston Globe reports.

Johnson missed Thursday's exhibition against Real Madrid with an illness, Adam Himmelsbach of the Boston Globe reports.

Analysis:

A bug has been working its way around the Celtics locker room recently, so it's possible Johnson will be isolated from the team for a few days until he shows improvement with his condition. The illness shouldn't jeopardize Johnson's availability for the majority of what remains of the Celtics' preseason schedule, but the big man's chances of opening the regular season in a starting role appear to have dissipated. Coach Brad Stevens has used David Lee and Tyler Zeller as his starting frontcourt for both of the Celtics' exhibitions thus far, leaving Johnson, Jared Sullinger, Kelly Olynyk, and Jonas Jerebko to fight for reserve minutes.