The New England Patriots placed linebacker Jerod Mayo and running back Stevan Ridley on injured reserve, ending their seasons.
Both players damaged their right knees in last Sunday's victory at Buffalo.
New England signed offensive lineman Chris Barker and running back Jonas Gray from the practice squad to the 53-man roster.
Mayo is one of the Patriots' leaders on defense, but played in only six games last season before tearing his pectoral muscle.
Ridley has rushed for 340 yards and two touchdowns this season, his fourth in the NFL. He ran for 1,263 yards in 2012, but had not been as effective since that season.
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