10:40 AM -- Fournette was driving his 2017 Maybach at the time of the crash and the bumper was wrecked.

But get this ... he signed the busted bumper and GAVE IT to first responders ... this according to WJXT4's Vic Micolucci.

Close call for Jacksonville Jaguars superstar Leonard Fournette -- who was rear-ended on a Florida interstate ... but he's OKAY!!!!

It all went down Tuesday morning ... a rep for the Jags says Fournette was "involved in a minor car accident today when his car was rear ended."

"Leonard is okay and was able to drive home."

The rookie running back -- who was a big factor in the Jags' playoff win over the Steelers this past Sunday -- was traveling on I-295, about a 10 minute drive from the EverBank Field.

And.... exhale.