Mathis signed with Washington early last month, making him the only player from another team to join the Redskins during an unusually quiet free agency period before the draft. He made his practice debut during this month's minicamp.
Mapu had 65 tackles, three sacks, two forced fumbles and two fumble recoveries in four years at Tennessee. He attended the minicamp on a tryout basis.
Mathis made the Pro Bowl as a returner with the Houston Texans in 2005, but he was injured for most of the last two seasons and had two recent run-ins with the law. He became a free agent when the Texans opted not to make him a qualifying offer at the end of last season.