RENTON, Wash. (AP) -- Seattle Seahawks rookie guard John Moffitt has been suspended for four games without pay for violating the NFL's policy on performance-enhancing substances.

The league announced the suspension on Tuesday. Moffitt will serve the suspension beginning immediately, even though he is currently on injured reserve and out for the season with a right knee injury.

The specifics of why Moffitt was suspended were not released.

Moffitt was Seattle's third-round pick in last April's draft out of Wisconsin and started the first nine games at right guard before suffering a pair of torn knee ligaments in Seattle's Week 10 win over Baltimore. He's one of three starting offensive linemen currently on injured reserve for the Seahawks, along with right tackle James Carpenter and left tackle Russell Okung.