Green but it's close. LINK
Over the course of 25 years, Darrell clocked a 44.3 second 400-meter dash, 20.5 second 200-meter dash, 10.08 second 100-meter dash, and a 4.15 40-yard dash. In the summer of 2004, at the age of 44, Darrell showed that his techniques still work when he recorded a 4.36 40-yard dash during a running demonstration at a youth summer football camp.
However..Deion Sanders ran an electronically timed 4.27 forty at the 1989 Combine which still stands I think.
Green was the only undefeated, 4-time winner, of the NFL's Fastest Man contests, which Green won I believe from 1988 through 1991. Deion should've challenged Green one of those times.
This post was edited on 1/27 at 8:17 pm