The Bulls announced Thursday he is out until at least late November.
Portis — averaging 10.5 points in his fourth season — joined a lengthy list of injured Chicago players in the fourth quarter of Wednesdays win over Charlotte.
Point guard Kris Dunn suffered a similar injury to his left knee in a loss at Dallas on Monday. He also missed the first two games for the birth of his first child. Lauri Markkanen is out until at least mid-November because of an elbow injury. And Denzel Valentine (sprained left ankle) has not played.
Chicago is 1-3.
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