He's behind the dude in SWAG pink suit!

Check this out ... a bunch of NFL stars are hanging together in Kentucky right now -- gearing up for the Kentucky Derby.

Baker Mayfield's front and center -- with an incognito Tom Brady blending in behind him.

Indianapolis Colts QB Jacoby Brissett -- Tom's former backup -- is in the bottom left ... standing next to Julian Edelman.

Also in the mix ... ex-Patriots' Lonie Paxton and Dan Koppen.

TB12 is a regular at the Derby -- so is his coach, Bill Belichick. Unclear if Bill has made it to Churchill Downs yet.

We already reported L.A. Rams head coach Sean McVay is in town with his smokin' hot girlfriend.