If Vince McMahon wants a big name in the XFL -- Chris Gronkowski says his little brother is down to lend his family crest to the league!
No, he ain't talking about Rob ... dude's kinda busy.
But Chris tells TMZ Sports his OTHER lil bro, Glenn, is totally game after getting waived by the Patriots during the regular season.
"He just got a Super Bowl ring last year, so sign him up!"
It's true ... Glenn (fullback) was a member of the New England Patriots practice squad last season.