Secretariat's Lock of Hair Hits Auction Block, Could Fetch $10K

A lock of hair from Secretariat -- arguably the greatest racehorse of all time -- has just hit the auction block ... and it can be all yours, if you've got a bunch of extra cash laying around!!

TMZ Sports has learned ... a 12-inch strand from the thoroughbred's mane that was obtained in the 1980s has just gone up for sale at Lelands -- and, experts there say it could sell for as much as $10,000.

We're told the piece of Secretariat's fur was gathered at Churchill Downs in the late '80s, when a groomer handed it over as a gift for a horse racing fan.

Of course, it's worth a bunch of money now considering Secretariat's incredible resume.

The horse was the 1973 Triple Crown winner ... and STILL holds the fastest time in all three races (Kentucky, Preakness, Belmont).

Secretariat -- who died in 1989 -- was inducted into the National Museum of Racing and Hall of Fame in 1974 and has statues at several stakes, including Belmont. The horse was also honored with a postage stamp in 1999.

There's also 263 roads in the U.S. named after him -- more than any athlete.

Opening price on the lock is $2,500, with bidding set to end Dec. 11.