He might be the welcher-weight champion of the world ... 'cause TMZ Sports has learned Antonio Tarver was sued over unpaid gambling debts by TWO VEGAS CASINOS before his problems with the Wynn.
According to court docs, Tarver got into some trouble with the MGM Grand and the Bellagio back in 2009 after taking out a heavy-duty gambling marker at each hotel and failing to pay it back.
MGM Grand says ... Tarver borrowed $100k but only paid back $10k
Bellagio says ... Tarver borrowed $50k but only paid back $5k.
They sued -- and according to court records, both casinos got their money back two years later.
But Tarver didn't learn his lesson. As we previously reported, the 45-year-old was locked up for allegedly skipping out on a $200,000 gambling marker from the Wynn stemming from 2012.
Tarver suggested his friend would help him repay the debt -- as long as he gets back in the ring and starts boxing again.
We spoke to Tarver's reps who insist the guy does NOT have a gambling problem.