GLENDALE, Ariz. -- The Arizona Cardinals have activated tight ends Jermaine Gresham and Troy Niklas.

Gresham, coming off back surgery, was on the physically unable to perform list, and Niklas, out with a hamstring injury, was on the non-football injury list.

The Cardinals signed Gresham to a one-year contract on July 24. Niklas, a second-round draft pick out of Notre Dame last year, has been plagued by injuries in his brief NFL career.

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Coach Bruce Arians said both will be limited to walkthroughs for now.

Arians also said rookie outside linebacker Shaq Riddick aggravated a hamstring injury. Arians called it a grade 2 tear and said Riddick, a fifth-round draft pick out of West Virginia, will be out for "some time."