World number one Lindsay Davenport has pulled out of the United States team for this week's Fed Cup semi-final against Russia with a back injury.
"I'm very disappointed that Lindsay would not be able to support our team here in Moscow," U.S. captain Zina Garrison told a news conference on Wednesday.
Garrison said that Davenport, who was treated for a back injury in the third set of her defeat by fellow American Venus Williams in the Wimbledon singles final, could not recover in time to face the defending champions.
Jill Craybas, who pulled off a shock at Wimbledon when she upset Serena Williams in the third round before losing to Venus, has been called in as a replacement.
Davenport's withdrawl is a huge blow for the Americans, who were already missing the younger Williams sister.
The former world number one pulled out of the tie at the Olympic arena following her tearful defeat at the All England Club last month.
She has been plagued by various injuries this season.
In the absence of Davenport and Serena, newly-crowned Wimbledon champion Venus along with doubles specialist Corina Morariu and Mashona Washington will carry the U.S. hopes in Moscow.
The Russians are also missing U.S. Open champion Svetlana Kuznetsova and French Open semi-finalist Nadia Petrova, who pulled out with shoulder and leg injuries respectively.
Last year's French Open champion Anastasia Myskina and beaten finalist Elena Dementieva will lead the home team.
The winners will face France or Spain in the Fed Cup final on September 17-18.