Dave Grohl -- Breaks a Leg On Stage ... FOR REAL!!! (VIDEO)

Dave Grohl just might be the toughest man in Sweden ... after falling off stage and breaking his leg -- he somehow managed to power through and keep the concert going.

According to Swedish witnesses (thanks Google translate) ... it seems the Foo Fighters frontman jumped down from the stage early on during the band's concert Friday night, and sustained a serious injury.

Dave kept singing, but once the song was over ... he waved the white flag, and said they were cutting the show short so he could get medical attention for what he assumed was a broken leg.

PSYCH!!!

FF kept rocking anyway, with Taylor Hawkins singing -- and a few songs later Dave returned with his leg propped up, and finished the concert. Best of all ... one of the songs he belted out was "Under Pressure."

As one fan put it, "Det kallar jag en riktig rockstjärna!"

Exactly.

The band posted Dave's x-ray. We're no doctors, but it looks like a busted fibula.