UFC fighter Devin Powell is one bro who won't be getting lucky on Valentine's Day -- 'cause he's in the hospital nursing a surgically-repaired nut.
No, we aren't making this up ... and Devin gave TMZ Sports the cringy play-by-play of the accident.
Devin told us he was training his ground game with UFC vet Joe Lauzon ... and it was business as usual until Joe's knee sandwiched one of his testicles and "exploded it."
"The top of it felt like a big sack of worms -- all the veins had swelled," Powell said.
The worst part -- Powell says he waited A DAY AND A HALF before getting his ruptured ball checked out.
Lucky for him, it wasn't too late. Devin says the scrotal surgery was a success ... and he's already asking Dana White to book him on an upcoming UFC card!
Seriously, the balls on this guy ...