The world number four was forced to miss Russia's Fed Cup final victory over Italy [Images] this month because of the injury, which she has been carrying since March.

Sharapova, the former Wimbledon and U.S. Open champion, will not play again until the season-ending championships in Madrid at the earliest, Stuttgart organisers said in a statement.

Nine of the world's top 10 women are still scheduled to play in the Stuttgart event.