Multiple independent witnesses tell TMZ Sports ... they each spotted Johnny Manziel partying well past midnight at a Cleveland bar on Friday ... just hours before he missed a team treatment session.

Our sources -- and they're pretty solid -- all say Manziel was hanging out and drinking at Barley House in Cleveland with a small party (3 to 4 other people) and didn't leave until 1:30 AM on Saturday morning.

We're told ... Johnny's group was seated in a "secluded VIP-kind of area" ... and sipped on vodka and champagne -- racking up a bill close to $1,000.

One source snapped a photo ... and though it's not the greatest quality ... it sure does look a lot like Johnny Football. The meta-data on the pic says it was shot at 1:21 AM on Saturday morning.

Manziel spoke to the media on Monday and denied reports that he "threw a party" that night -- but it seems like the 22-year-old is just arguing semantics at this point.