Millsap suffered the injury last week when he banged knees with Detroit's Greg Monroe in a loss to the Pistons last week. He limped to the bench but later returned to the game. He then missed the next three games and his status for the remaining four games of Atlanta's upcoming road trip is uncertain.
Millsap has appeared in 53 games this season and is averaging 17.6 points and 8.3 rebounds.
Atlanta did get a bit of good news as Pero Antic was limited in practice on Friday. No word on whether or not this was Pero's official return to practice in any capacity but the team has updated his status to day-to-day.
Gustavo Ayon had season-ending shoulder surgery on Thursday so the newly signed Mike Muscala figures to get an opportunity right away to contribute.