Robles will receive an MRI on his left hamstring Thursday, Mark Zuckerman of MASNSports.com reports.
Robles appeared to tweak his left hamstring while running to third base during the second inning of Wednesday's win over Pittsburgh. More will be known about the severity of his injury once the MRI results come back Thursday, but a stint on the IL may be necessary for the 26-year-old. Ildemaro Vargas entered the game as Robles' replacement and could be in line for more outfield work if Robles ends up on the injured list, though it's possible the Nationals recall Jacob Young or Alex Call from Triple-A Rochester to make up for the lost outfield depth.