EXCLUSIVE

It was supposed to be the wrestling match to end all wrestling matches -- Hulk Hogan vs. John Cena in a battle royale -- but it was all dashed to pieces thanks to some bogus back surgery ... according to Hulk Hogan ... and it cost him $50 MILLION.

TMZ broke the story ... Hulk filed a $50 million lawsuit against the Laser Spine Institute of Florida -- claiming its doctors duped him into undergoing multiple procedures in 2009 that were completely useless and damaged his career.

Hulk doesn't explain why he's suing for $50 million in the lawsuit -- but Hulk's legal team (headed by Wil Florin) tells TMZ, the reason for the massive sum is a lucrative "phase out contract" that was torpedoed by the bad surgeries.

According to Hulk's team, the contract outlined a blowout match between Hulk and Cena -- a match that was supposed to be Hulk's career ender -- but thanks to the surgeries, it never happened.

Hulk's claiming the contract -- along with subsequent appearance opportunities -- was worth $50 million.