The injury appeared to occur after Isaac jump-stopped past two opponents and planted on the floor in an awkward fashion:
"It looked bad, obviously," Orlando coach Steve Clifford said after the game, per ESPN's Ohm Youngmisuk. "Until you hear anything, I am just hopeful, that's all."
An MRI performed after the game revealed the full extent of his injury.
Once word of Isaac's diagnosis broke, the Magic forward received an outpouring of support from his peers:
The loss of Isaac is a major one for Orlando. The 22-year-old is averaging 12.1 points, 6.9 rebounds, 2.4 blocks, 1.5 steals and 1.3 assists in his third season, all career highs, while shooting 47.1 percent from the field and 34.4 percent from three.
Isaac's offensive game remains a work in progress, but he's been a defensive difference-maker for the 32-35 Magic, who beat the Kings 132-116 on Sunday and currently hold the No. 7 seed in the Eastern Conference standings.
"My whole heart goes out to him. He's such a great guy, such a great person," Isaac's teammate Aaron Gordon told reporters after the game. "... I hope it's nothing serious. I hope it's just something that kind of shocked him. But it was sad, man. It brought tears to my eyes."
Isaac's 2019-20 season has been hampered by injuries. He missed 31 games with a left knee injury before the NBA was shut down because of the COVID-19 pandemic, the same knee he injured Sunday.
There's now a possibility that he'll miss a large chunk—if not the entirety—of the 2020-21 season, which is expected to begin in December. That would be an enormous setback for him.