A baseball that’s roughly a decade old is about to sell for thousands of dollars … and it’s all ’cause Patrick Mahomes put his “John Hancock” on it way back when he was a high school senior!!

The ball was just discovered at a thrift store in Rockwall, Texas last month … and it’s super cool. It features signatures from some of the players who took the diamond in Texas for the Whitehouse H.S. Wildcats during the 2013-14 season.

In total, there are six names scribbled on it … but, of course, none is bigger than Mahomes — who put a “#5” next to his autograph when he inscribed the sweet spot.

Leland’s just put the piece on its auction block — and while bidding has started at $2,500 … TMZ Sports is told it could fetch $10,000 and up!!

While it might sound a little crazy — considering Mahomes, after all, does play football … it’s actually not the first Mahomes-autographed H.S. baseball that’s sold for a wad of cash.

Back in 2020, one that the Chiefs star and the rest of his Whitehouse teammates signed in 2013 netted its seller a whopping $6,510.

Seems like a ton of cash … but, hey, an autographed baseball signed by Michael Jordan during his high school days did go for $36,000 — so it doesn’t seem to be a bad investment by any means.

Bidding officially closes on the Mahomes baseball in less than two weeks … good luck!!