Following a practice session, Roddick and his trainer determined that the strain was still affecting the American's game.

    "Andy and athletic trainer Doug Spreen determined that Andy was still not fit to compete without risking further injury," said a statement posted on Roddick's website.

    The former world number one suffered the injury in the closing stage of a second-round victory in Los Angeles over American Scott Oudsema.

    He came out unable to play in the next day's quarters against Russian Dmitry Tursunov, before withdrawing from this week's tournament in Washington

    "Unfortunately, my side strain is still preventing me from being able to play matches," Roddick said in a media release. "I will be working hard this week and am optimistic to be back in top form for the U.S. Open." Enditem