Mattison was released by the Chiefs Sept. 26 after being on the team's roster for one game. He previously spent time with the St. Louis Rams, making four starts and appearing in 15 total games in 2011. He was on the Baltimore Ravens practice squad from 2008-09 before making the team in 2010. Mattison was an undrafted free agent out of Iowa, first signed by the New York Jets in 2008.
Thorpe was called off the Chiefs practice squad for the Chiefs' Week 5 game against the Ravens. Undrafted in 2012 out of Auburn, Thorpe played in special teams in his only appearance this season. Baltimore defeated Kansas City, 9-6, in that game, dropping the Chiefs to 1-4 on the season.
The Chiefs will next travel to Tampa Bay to take on the 1-3 Buccaneers in Week 6. Heading into that game, it appears quarterback Matt Cassel will be ruled out with the concussion he suffered against the Ravens.