It's an ultra-rare signed Giannis Antetokounmpo basketball card that features a piece of a game-worn jersey from the Greek Freak's rookie season.

The card was originally pulled out of a pack of Panini America's 2013-14 high-end "National Treasures" line ... and features the NBA "Logoman" patch from one of Giannis' rookie jerseys.

It's a 1-of-1 card -- so, it's super rare -- but the fact it was graded a MINT 9 by the Beckett Grading Service makes it even more desirable for hardcore collectors.

Even better ... the signature on the card received a perfect "10" grading from the Beckett autograph evaluators as well.

Again, the high-grading number makes a HUGE difference for collectors at the high-end level.

The person who initially pulled the card from a pack years ago sold it to another collector -- and after changing hands a few times, it's now hitting the auction block over at Goldin Auctions, where they believe there's a strong chance it could break the record for most expensive basketball card ever sold.

Of course, a rare (and similar) LeBron James' 2003-2004 Upper Deck rookie card is currently the G.O.A.T. piece when it comes to basketball cards ... it famously sold for $1.8 MIL last month.

The LeBron card was NOT a 1-of-1 -- there were 23 of those made ... and Bron has bragged that he has a few sitting around at his home.

The rare-card market is ON FIRE right now -- a Topps 2009 Superfractor Mike Trout card just sold at auction for $3.93 mil ... the most expensive sports trading card to ever sell on the open market.

As for Giannis, the bidding began at $250k on Monday -- and after a flurry of quick bids, it's already about to crack the $500,000 mark!!!

Ken Goldin, who runs Goldin Auctions, says he wouldn't be surprised if it cracked $2 mil by the time the bidding ends on Sept. 20th.

Remember when everyone said the trading card market was dead?!