... well, the Seattle Seahawks receiver is now taking his speed to a real track -- signing up to sprint in the 100m race at the USTAF Golden Games and Distance Open on Sunday at Mt. SAC.

No joke! The 6'4", 229 pound Pro Bowler will put his speed to the test on May 9 against 16 experienced sprinters in Walnut, California.

And, we mean experienced -- Ronnie Baker is one of the 16 runners and that dude ran a 9.94 in the 100m earlier this year!!!

Keep in mind, Metcalf hasn't competed in a legit track competition since high school -- where his best event was the hurdles and the triple jump (though he also ran the 4x100 relay).

But clearly, DK has world-class speed -- which he put on display back in October when he sprinted 90 yards to chase down fleet-footed AZ Cardinals defensive back Budda Baker, one of the fastest guys in the league.

And, don't forget, he also clocked a 4.33 in the 40-yard dash at the 2019 NFL Combine -- which is insane for someone of DK's size.

The big question ... is DK fast enough to make the US Olympics team? Maybe!

DK would have to crack the 10.05 mark in the 100m race to qualify for the Olympic Trials, according to the USATF.

Yeah, he's a long shot but DK is confident -- even dropping a teaser clip on his social media page.