The story was first reported by SiriusXM.
Gore, who will turn 35 in May, rushed for 961 yards for the Indianapolis Colts in 2017, just shy of a 10th career 1,000-yard season.
He moved ahead of three Hall of Fame running backs and into fifth place on the NFL's career rushing list last season. He enters his 14th season with 14,026 career rushing yards and needs just 76 yards to pass Curtis Martin for fourth.
Gore signed with the Colts in 2015 with the goal of pairing with quarterback Andrew Luck. Injuries to Luck, however, limited the two to only 22 games together in Gore's three seasons in Indianapolis.
ESPN's Mike Wells contributed to this report.