EXCLUSIVE

If Gabby Douglas wants to cash in on her "Flying Squirrel" nickname ... she's gonna have to battle a college kid who locked up the trademark while Gabby was still competing in the Olympics.

TMZ has learned ... Fordham University business student A.J. Rotonde filed to trademark the phrase on August 6 with the U.S. Patent and Trademark office for a mere $325.

Rotonde tells us he decided to scoop up Gabby's handle after watching her destroy the competition in London.

A.J. has NO connection to Gabby or U.S. gymnastics, but tells us he plans to slap "Flying Squirrel" on T-shirts and other merchandise -- but before he cashes in the USPTO has to approve his application ... which could take several months.

Gabby can still challenge A.J.'s filing and apply to trademark the phrase herself.

A.J. tells us he'd be happy to sell the TM back to the gymnast ... for the right price, of course.