The Cardinals placed Watkins (biceps) on injured reserve Saturday, Darren Urban of the team's official site reports.
Watkins sustained the injury in Week 2 against the Giants. He signed with the Cardinals in March after spending the past two seasons with the Cowboys. Watkins will now be forced to miss the next four games and will be eligible to return in Week 7 against the Seahawks on Oct. 22, though he could miss more time while recovering from his injury.