Glen Davis: Hardcore Training In L.A. For NBA Return

Beware, NBA forwards ... you might have a 6'9", 300 lb problem ... 'cause TMZ Sports has video of Glen "Big Baby" Davis putting in some serious work in hopes of making an NBA comeback.

Davis hasn't been in the league since the 2014-15 season ... but he wants back in -- and we've got footage of the guy busting his ass at the Sports Academy in Thousand Oaks, CA.

We're told Davis has been training at the S.A. 5-6 days a week -- working with a full team of specialists focusing on strength and endurance. He's also got a nutritionist and a "mindset development guru."