Robles (back) is set to begin a rehab assignment Thursday with Triple-A Rochester, Mark Zuckerman of MASNSports.com reports.
Zuckerman writes that Robles "could spend up to a week" on the farm getting back into baseball shape. He's been out for a full month because of a lingering back injury. Alex Call continues to serve as the Nationals' primary center fielder. He could serve as Washington's No. 4 outfielder whenever Robles is activated.