The man who got pummeled by Kourtney Kardashian's ex says he's going to sue Drake and Odell Beckham Jr. ... because he believes they're responsible for the attack.

The victim -- Bennett Sipes -- has lawyered up and they don't just have Kourtney's ex, Younes Bendjima, in their crosshairs. TMZ broke the story ... Younes beat the crap out of Bennett outside Delilah restaurant in WeHo back in March, as Drake, Odell and their posses looked on.

THE BRUTAL BEATDOWN
TMZ.com

Sipes' lawyer, Colin Jones at the Wilshire Law Firm, tells TMZ ... he learned from speaking to his client and witnesses that his client's girlfriend -- famed Instagram model Sommer Ray -- was hanging in the VIP section of the club during the evening, chatting with Odell. Toward the end of the night, Sipes -- who was an employee of Delilah, but not working that night -- went to the VIP section to get his GF, and Odell was none too pleased.

What happened next is unclear. It seems words were exchanged, but it did not get physical. Cut to around 2:30 AM, when Drake, Odell and their crews left through the back door. That's when Sipes appeared, said something, and Younes unleashed a barrage of punches, and was joined by another man.

Attorney Jones believes the other man who began punching was a member of either Drake's or Odell's security team, which would make them responsible for what the guy did.

Sources connected with the group say Sipes was the aggressor in the VIP area, and incited them as they left. They also say Drake and Odell had nothing to do with the fight.

Jones said he had no idea Younes was the guy who delivered the initial flurry of punches until he saw the video we posted Wednesday, and that was enough to commit to a lawsuit.  

Sipes was pretty badly beaten as you can see. Jones says his client is still going through physical therapy, months after the attack. 

As we reported, Sipes went to the L.A. County Sheriff's Dept. and filed a police report, but has been uncooperative since ... so the investigation's closed.