Maria Sharapova has pulled out of her Italian Open semi-final against Jelena Jankovic with a calf injury.

The Russian was due to face the Serb defending champion on Saturday.

She came through a tough match against Patty Schnyder late on Friday night in which she lost the first set but fought back to triumph 6-7 (3-7) 7-5 6-2.

Jankovic will meet either sixth seed Anna Chakvetadze or French qualifier Alize Cornet in Sunday's final.

Despite her pull-out, Sharapova will be confirmed as the world number one in the new WTA rankings on Monday after the surprise retirement of Justine Henin.