Johnny Manziel -- Checks Into Rehab

Johnny Manziel has checked into a treatment center ... this according to multiple members of Manziel's camp.

A rep for the Cleveland Browns issued a statement saying, "Brad Beckworth, friend and advisor to Manziel and his family, has confirmed that Johnny entered treatment on Wednesday."

"Johnny knows there are areas in which he needs to improve in order to be a better family member, friend and teammate and he thought the off-season was the right time to take this step."

"On behalf of Johnny and his family, we’re asking for..privacy until he rejoins the team in Cleveland."

The Browns did not say exactly why Manziel is being treated -- but it seems pretty obvious ... considering his penchant for partying.

Earlier this season, ESPN's Skip Bayless said he'd spoken with several people close to the Browns QB and was convinced Johnny is an alcoholic.

Johnny responded to the criticism by hitting the bar scene -- and after the season, was seen chugging champagne at a hotel pool.