Ruiz said Brown owed him $10K, but he couldn't get the cash from the football player -- even after talking with Brown's attorney.
So, Ruiz ended up going public with his claims that Brown had sought and obtained a fake vaccine card and then later submitted it to the NFL.
The league investigated the claims ... and said it found Brown did misrepresent his vaccine status, and then suspended him three games without pay, costing him over $100K in lost salary.
Ruiz tells us if Brown had just paid up, he probably would've stayed quiet.
"If he had just probably paid me, you know what? He probably would still be getting paid in the NFL right now," Ruiz said. "He'd probably be playing the games that he could be playing and none of this would have even happened."
As for Brown, he's claimed through his attorney, Sean Burstyn, that he is vaccinated ... although the NFL says Brown will not appeal his suspension.