Riley suffered a slight Achilles tear during Wednesday's practice, Rick Stroud of the Tampa Bay Times reports.
Riley's signing a contract with the Buccaneers, Greg Auman of The Athletic reports.
The Vikings waived Riley on Saturday.
Riley is set to sign with the Vikings on Thursday, Field Yates of ESPN reports.
The Cardinals waived Riley on Tuesday, Darren Urban of the team's official site reports.
Defensive coordinator Vance Joseph said Thursday that Riley will start during Sunday's game against the Panthers, Kevin Zimmerman of ArizonaSports.com reports.
Riley signed a contract with the Cardinals on Thursday.
The Steelers waived Riley on Sunday.
The Steelers signed Riley to a contract, Ian Rapoport of NFL Network reports.
Riley had 34 tackles (27 solo), one pass defensed and one forced fumble in 16 games this season.