Gado, 25, spent last season with the Houston Texans. He ran 35 times for 104 yards and three touchdowns, and added four receptions for 47 yards.
The team also placed wide receiver/kick returner Dante Hall on injured reserve after he suffered an ankle sprain in Sunday's loss to the Cardinals. He made only 12 catches for 105 yards on the season.
Drew Bennett, who made only one catch in the season opener before breaking his leg, also was placed on injured reserve.