Red Bull who, Monster what?? Saquon Barkley is entering the energy drink game in a big way ... buying an ownership stake in X2 Performance, TMZ Sports has learned.
We're told 24-year-old Barkley -- who missed most of last season with a torn ACL -- spearheaded a round of funding totaling $15 million ... making Saquon an owner in the growing brand.
Before bringing Barkley on board, X2 wasn't lacking star power ... NBA MVP Kawhi Leonard is also a part-owner of the company.