Underwood, 24, spent the previous two seasons with Jacksonville and totaled eight catches for 111 yards and 24 kick returns for 561 yards. He had been signed and released twice by the Patriots earlier this season.
Rookie linebacker Jeff Tarpinian was placed on injured reserve with a head injury. Over seven games he totaled 12 tackles on defense and special teams.
Also on Thursday, the team signed safety Ross Ventrone to the practice squad and released defensive back Josh Victorian from the practice squad.