The Cardinals placed Prater (knee) on injured reserve Tuesday, Darren Urban of the Cardinals' official site reports.
Prater's left knee injury had already cost him the Cardinals' last two games, with Arizona elevating Chad Ryland from the practice squad to serve as its kicker on both occasions. The Cardinals had been hoping for an abbreviated absence from Prater, but with the 40-year-old not bouncing back as quickly as hoped, he'll now have to miss at least four more games. Ryland was signed off the practice squad to take Prater's spot on the 53-man roster.