If you're gonna pick a fight with a hockey player, STAY AWAY FROM BRIAN MCGRATTAN ... so says Calgary Flames captain Mark Giordano

We were talking to Mark about which hockey player would have the best shot at success in the UFC -- and without hesitation, Giordano brought up the legendary enforcer.

"I've never seen him lose a fight," Mark explained. 

McGrattan -- 6'4", 235 lbs -- had a helluva fight record during his time in the NHL ... and is said to have not lost a single scrap during the 2013-2014 season despite playing in 76 games.

Here are some highlights. Enjoy the violence.