Johnny Manziel -- Drinks Thrown at QB ... at Houston Nightclub

Johnny Manziel was attacked with drinks at a Houston nightclub this weekend ... after the Cleveland Browns QB got into it with a group of hecklers ... TMZ Sports has learned.

It all went down at Dekan nightclub in Houston late Sunday night -- Manziel arrived with some friends looking to have a good time when things got chippy.

We spoke with J.R. from Sticky Promotions -- who was with Johnny that night -- and he tells us people were shouting at Manziel and aggressively trying to take pics.

At one point, a frustrated Manziel flipped off one of the hecklers -- and that's when J.R. says the drinks started to fly.

"I ducked and I looked at Johnny and we grabbed security and they ran us out of there," J.R. says.

We're told Johnny and some members of his crew were splashed with drinks -- so they went back to their hotel room to change.

J.R. says he spoke with club security -- who told him the drink-throwers were booted from the joint -- so Johnny and his posse decided to return to the club.

Once they got back inside -- with Manziel wearing a new shirt -- we're told Johnny partied without incident for the rest of the night and had a great time.

We spoke to Houston PD -- and we're told cops were never contacted about the incident.