49ers Star Kyle Juszczyk Training Like Rocky In Quarantine, Tree Trunk Squats!

Think quarantine is gonna stop S.F. 49ers star Kyle Juszczyk from training to get back to the Super Bowl???

HELL NO!!! The Niners fullback is doing straight-up Rocky-style workouts while in isolation ... squatting a whole damn tree in the snow!!!

Juszczyk's smokin' hot wife posted the footage of the 28-year-old getting in lifts out in the wilderness ... and it's pretty intense.

You can see in the videos, Juszczyk sled-pulls his wife (and others) through snow AND dirt to get some leg work done.

Then, the 6-foot-1, 240-pound NFL player gets some jump squats in ... with a dead tree on his back!!

"When the gyms are closed but Kyle still needs go workout!" Kyle's wife, Kristin, said. "😂😂"

Of course, Kyle's on a mission this offseason ... his Niners came THIIISSSS close to being Super Bowl champs last month -- and the window to try to do it again is still open.

By the way, when Kyle's not working out like a madman ... it's safe to say he ain't exactly suffering in isolation -- 'CAUSE HAVE YOU SEEN HIS WIFE?!?