UCLA's Myles Jack -- Drops Out of UCLA ... Declares for NFL Draft

School's out for UCLA superstar linebacker Myles Jack -- because the college football star just announced he's dropping out of college and will enter the NFL draft.

It's interesting timing for Jack -- who just suffered a season-ending knee injury last month -- since college football season is still underway.

20-year-old Jack -- a junior who was one of the most highly touted players in the country before the season began -- suffered a torn meniscus during practice on September 23.

Jack doesn't seem to be getting support from his head coach Jim Mora ... who told the media, "I think it's very risky to do this. There's a lot of speculation to ... where he fits."