NBA's Jonathan Isaac Tears ACL 2 Days After Anthem Standing Demonstration

Jonathan Isaac -- the Magic player who stood for the national anthem and did not wear a BLM shirt before Orlando's game last Friday -- has torn his ACL and will miss the rest of the season, the team announced Sunday.

Isaac gained national attention just 3 days ago ... when he became the league's first player in the NBA bubble restart to stand for the anthem.

Wearing his Magic jersey and warmup sweats ... Isaac stood with his hands behind his back and bowed his head during the song -- and after the game, he explained he didn't participate in the demonstration with his teammates for religious reasons.

But, Isaac, playing in just his second game since the Friday gesture ... drove the lane against the Sacramento Kings on Sunday and blew out his knee.

The video is tough to watch ... Isaac's leg buckled -- and afterward, the Magic said the 22-year-old is now "out indefinitely and his return to the court will depend on how he responds to treatment and rehabilitation."

Isaac had started 32 games for Orlando this season ... and averaged 11.9 points per game and 6.8 rebounds per game.

Only one other player, meanwhile, followed in Isaac's anthem-standing footsteps in the NBA's restart this past weekend ... Miami Heat's Meyers Leonard also stood for the song before his game Saturday.

After the move, Leonard -- who said he supports the BLM movement -- told ESPN, "Our world right now is black and white. There is a line in the sand, and it says if I don't kneel, then I'm not with Black Lives Matter. That is not true."

Spurs head coach Gregg Popovich also chose to stand for the anthem before San Antonio's game Friday night as well.