Cleveland Browns superstar Joe Haden is such a huge sneakerhead -- HE JUST BOUGHT AN ENTIRE STORE ... and TMZ Sports has learned he's having a massive grand opening party on Black Friday!

Here's what we know ... Haden has been wanting to get into the shoe biz for a while -- and bought out an existing sneaker shop in downtown Cleveland, which he renamed "The Restock."

We spoke to Joe's business partner David Damier, who tells us ... "It's a consignment-based store. We specialize in offering shoes that you can no longer find in stores. Rare shoes are our specialty."

Doors open on Black Friday -- and David says Joe will definitely be on hand to celebrate ... even though the Browns have a game in Atlanta that weekend.

"They don't fly out until Saturday, so Joe will definitely be there. There will be a bunch of athletes there."