Tommy Fury left a TON of money on the table this year ... with a new documentary revealing TNT had the chance to fight Jake Paul again in June -- but he turned it down due to timing.
The nugget of info was documented in the new project, "Tommy: The Good. The Bad. The Fury" ... where a scene shows the boxer's dad, John, taking a call from their lawyer during a camping trip.
In the chat, the two discuss how Paul's original opponent backed out .