UFC Fighter Joe Riggs -- I'll Fight Again ... Even with Holes in My Hand and Leg

UFC fighter Joe Riggs has a huge hole in his leg, and another in his hand ... but he's still vowing to fight again as early as December -- which is unbelievable when you see how badly his hand was injured in a gun accident.

TMZ Sports broke the story ... Riggs was cleaning his Sig Sauer 1911 pistol last month when the weapon discharged, blowing a hole in his left leg. He also severely jacked up his left hand. Fair warning ... these pics of the damage are gruesome.

We're told Riggs' doctors are only willing to say he will "eventually" make a full recovery -- but the fighter is confident he'll be ready to go before year's end.