UFC fighter Devin Powell is one guy who won't be getting lucky on Valentine's Day ... dude's in the hospital nursing a surgically-repaired nut.
No ... we're not making this up.
Earlier this week, Devin was training with UFC vet Joe Lauzon at his MMA gym in Maine ... and says they were practicing knees on the ground.
You can guess what happened next.
The worst part -- Powell says he waited A DAY AND A HALF before getting his "ruptured testicle" checked out.
Lucky for him, it wasn't too late.