TMZ Sports obtained the clip, which features Fournette saying he would "whup your ass" to a fan. On Monday, Jaguars head coach Doug Marrone told reporters the fan directed a racial slur at the running back before the threat.
Fournette later told Daniel Popper of The Athletic that the fan called him a "coon" and a "servant."
"It wasn't called for," Fournette told Popper.
"Facts, you're too old for that," Fournette said on the video. "You're too old for that. Chill out. I'm not worried about you. You want to come down here? I'll whup your ass."
Fournette had come over by the fans and threatened a fight earlier in the game before being pulled away by two team staffers.
The Titans held Fournette to 36 yards on 14 carries in a 30-9 victory. Fournette watched on as Derrick Henry dominated the Jags defense to the tune of 238 yards and four touchdowns.
The 2018 season has been a major disappointment for Fournette from an individual and team perspective. He's posted just 350 yards and four touchdowns on 104 carries while sitting out seven games due to injury.
The Jaguars have lost eight of their last nine games after a 3-1 start.