Philadelphia 76ers star Joel Embiid has been ruled out for Monday's Game 1 of the Eastern Conference semifinals against the Boston Celtics due to his knee injury, ESPN's Adrian Wojnarowski reports.

Embiid hurt his knee in Game 3 against the Brooklyn Nets in the first round of the playoffs. He tripped over Nets guard Cam Thomas while contesting a drive, and their limbs twisted as they fell down. Embiid got up and stayed in for the rest of the game, but visibly limped and wasn't very effective.

The Sixers ruled Embiid out for Game 4, which they were able to win without him. But sweeping the Nets is a different beast than taking on the Celtics. Philly knows that firsthand. The Sixers faced the Celtics in the playoffs in 2018 and 2020, and their record is a pathetic 1-8 in those two series. Philadelphia needs Embiid to get better — historically a tough task for him in the playoffs — or it may have trouble seriously challenging Boston.

At this point, we don't know when Embiid will be back. According to Shams Charania of The Athletic, Embiid's reported LCL strain is more serious than first thought, and he apparently underwent a platelet-rich plasma treatment last week. However, ESPN's Adrian Wojnarowski reported that there's optimism he could play in Game 2 on Wednesday night.

Game 1 of the Eastern Conference semifinals will air Monday at 8 p.m. ET on TNT.