The Heat locker room's televisions have been showing the NFL Scouting Combine this week and James was asked what he could run the 40-yard dash in.
He says he ran the 40 in 4.6 seconds last summer.
"I was just messing around, though," James said, via ESPN.com. "No training."
"It's better than Manti Te'o, I'll tell you that," he said to the South Florida Sun-Sentinel.
Te'o, the former Notre Dame linebacker, ran a 4.82 at the combine this week.