The chef who told the NFL that Antonio Brown faked his COVID vaccine card is now planning to sue the Buccaneers star ... saying the wide receiver still owes him $10,000.

Steven Ruiz spelled it all out to TMZ Sports this week ... saying after the NFL ruled he wasn't lying about Brown's bogus vaccine card --- he's planning to move forward with a lawsuit against AB.

"The game plan now is to file a lawsuit and take it from there," Ruiz said. "People provide a service and you've got to pay for it. That's it."

As we previously reported, Ruiz said he cooked for Brown regularly this past year ... but when it came time to pay a bill for it all, AB balked.