WWE superstar Sheamus may not be a champ anymore, but he's still living like one -- dropping a bundle on the crown jewel for all exotic car lovers ... who also happen to love " Back to the Future ."

Our sources tell us the Celtic Warrior went searching for a DeLorean last weekend -- and hit up Just Toys Classic Cars in Orlando for a test drive. He clearly fell in love with it on the spot ... 'cause he scooped it up for around $55K.

Unclear if Seamus is a "Future" fanatic ... but he can forget about a road trip to 1955. The seller tells us the car -- which is more than 30-years-old -- has a "tough time getting to 88 miles per hour."