Rob Gronkowski's gettin' in on the EXPLODING digital sports memorabilia market ... the NFL superstar is releasing his own limited edition, virtual trading cards.
TMZ Sports talked to 31-year-old Gronk ... and the 4x Super Bowl champ broke the news on his new side hustle.
RG -- with biz partners Adam Richman and Joe Silberzweig -- linked up with artist Black Madre,Gronk's good friend ... and created 5 (very limited) trading cards.
But, no cardboard here -- the cards are part of a digital collection Rob's calling his Championship Series NFT Collection.
NFT stands for non-fungible token -- essentially a digital card that can't be duplicated -- and Gronk believes they're the future of the trading card world.
"I think having digital trading cards now is just gonna be unique and it's gonna blow it out of the water. Actual trading cards, I think will always be there, but I think it's leading towards a way where everything's digital."
Trading cards (and all sports memorabilia) have blown up over the last few years. In fact, a 1996-97 Topps Chrome Refractors Kobe Bryant rookie card just sold for $1.8 million.
Rob -- starting Thursday at 7 PM ET on crypto marketplace, OpenSea.io -- is dropping 5 cards featuring original, hand-drawn artwork ... celebrating his Super Bowl XLIX, LI, LIII, and LV championships.