Johnny Manziel -- Chuggin' Champagne ... During Miami Getaway

Johnny Manziel clearly does not think he's got a drinking problem ... 'cause the Cleveland Browns QB was chugging champagne right from the bottle in Miami on Wednesday.

Manziel and his girlfriend Colleen Crowley were sitting poolside at a Miami hotel ... sippin' away under the sun on Veuve Clicquot Rose'.

At one point, someone handed Johnny what appears to be a mixed drink -- and he took that down too.

Interesting move ... considering he's been under fire for reportedly missing an official team treatment session following a night of hard-partying.

In fact, ESPN's Skip Bayless went on the air and said he's convinced Manziel is an alcoholic after speaking with several people in the Browns organization.