Carl Lewis -- one of the greatest U.S. track athletes EVER -- says he would've eaten the 40-yard dash alive ... telling TMZ Sports his time would've been in the THREES!!!
"Track guys that run it, run it under 4. So, under 4 seconds. Yeah."
Obviously, that time is BLAZING fast ... in the NFL combine last month, only six guys even broke the 4.40 mark.
In fact, the fastest dude in the entire event was Mississippi safety Zedrick Woods -- who clocked in an official time of 4.29.
But Lewis tells us even though he's never ran it -- he's pretty sure he could've gotten into the 3s .