NAPA — Oakland Raiders wide receiver Javon Walker is back at practice for the first time since undergoing an offseason knee operation.

Walker had the procedure in April and has been on the physically unable to perform list for all of training camp. Walker has not said what kind of operation he had, saying only it was revolutionary and done outside the United States.

The Raiders are counting on Walker this season because he is one of the only experienced receivers on the roster. Rookies Darrius Heyward-Bey and Louis Murphy started the most recent exhibition game.

Walker had only 15 catches in his first year in Oakland, but has two 1,000-yard seasons in his other six years in the NFL.