4:00 PM PT -- Beers wasn't Gronk's only enemy at the parade ... TMZ Sports has video of the tight end trying to catch a football with his face ... and it didn't work out well.

Rob Gronkowski paid the price for partying at the Patriots' parade Tuesday ... WITH HIS BEAUTIFUL FACE!!!

The tight end says while he was celebrating New England's Super Bowl title ... some people tossed a bunch of booze at his duck boat -- and a full beer can caught him near his eye!!!

Gronk -- who was speaking with Jimmy Fallon on Wednesday's 'The Tonight Show' -- says the aftermath wasn't pretty ... "I was bleeding all over on the parade on the duck boat."

In fact, the beer shot rattled the dude so much ... Rob says his dad had to step in to block other flying objects while his son recovered!!!

Good news for Gronk and Pats fans ... he says he's fine now -- nothing but a scratch.

Flying beer cans at Boston parades have struck before ... remember when the Red Sox World Series trophy was damaged by a rogue Bud Light????

As for the hits Gronk took during the Super Bowl -- Rob seemed more concerned about those ... saying he actually had to cancel his initial appearance on Fallon 'cause he was so banged up.