Dwayne Johnson suffered a pretty gnarly gym injury Monday requiring stitches to close a wound on his face.

But, instead of cryin' about it -- he tasted his own blood and went right back to work!!!

The former WWE superstar said he suffered the wound throwing around some heavy weights -- and in a video, he revealed his eye was swollen and bloody.

But, in true tough guy fashion ... The Rock licked the blood off his face and said, "That's good. That's real good. Back to work."

!!!!!!

Johnson later explained he got nicked up tossing 50-pound chains ... and said the wound was so bad, he needed stitches.

Though the 48-year-old said he didn't go under the needle and thread until AFTER the workout was done ... 'cause, duh.

"We ain't playing tiddlywinks and we ain't reciting nursery rhymes," Dwayne said ... before later writing, "Taste your own blood, keep working out and stitch up later - rules of the house."

Who's ready for leg day now?!