Rob Gronkowski Hits Hollywood Club ... Leaves with Hot Blonde

Rob Gronkowski had a pretty great Wednesday night ... hitting up one of the hottest clubs in L.A. ... and leaving with a smokin' hot blonde.

The Pats tight end hit up Warwick with his regular party crew -- and left the joint just after 2 AM.

But after he got into the waiting SUV, a very attractive lady in a fire red dress followed the NFL star into the car ... and they drove into the night.