The Cavs were missing six regulars on Thursday night in a loss to the Golden State Warriors.
The injury is also a major setback for Sexton, who failed to get a contract extension from Cleveland before the 2021 opener and was hoping another solid season would lead to lucrative offers.
He'll become a restricted free agent next summer.
Despite Cleveland viewing Sexton as part of its young core with Mobley, point guard Darius Garland, center Jarrett Allen and forward Issac Okoro, his name was often mentioned in numerous trade rumors.
Sexton's game can be infuriating to teammates and opponents alike, as he's a ball-dominant player who can score but doesn't always make great decisions.
Now, his injury only further clouds Sexton's future with the Cavs, who drafted him with the No. 8 overall pick in 2018.
Sexton has improved in each of his four seasons. He averaged 24.3 points last year on a 22-win Cleveland squad.
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