Venus Williams has made herself unavailable for the USA's Fed Cup semi-final against Russia in Alabama this weekend because of injury.
Captain Mary Joe Fernandez had left a space open for the world number four but Williams has not yet recovered from the knee problem she aggravated in Miami last month.
Williams said in a statement to www.usta.com: "I am continuing to rehabilitate my knee and regret that I will not be able to participate in the Fed Cup tie against Russia this weekend.
"I waited until this moment in hopes that I would have an opportunity to play but I am being advised by my medical support team that I will need more time to recover.
"I will be rooting for a United States win and look forward to returning to Fed Cup competition."
With Williams' sister Serena, the world number one, also injured, Fernandez named rising star Melanie Oudin, Bethanie Mattek-Sands and doubles specialist Liezel Huber in the team to face Russia.
Promising youngsters Sloane Stephens and Julia Boserup travelled with the team for experience and one will now be added to the line-up as back-up.
Neither Williams sister has played Fed Cup since 2007, and Fernandez said: "We're kind of used to not having either Venus or Serena around, so it's not like a shock to the team that really disrupts it."
Meanwhile, the Russians have had their own problems with half their team stuck in Russia because of the flight problems in Europe.
Elena Dementieva and Ekaterina Makarova have been practising in Birmingham, with captain Shamil Tarpischev, Anastasia Pavlyuchenkova and Alla Kudryavtseva due to arrive overnight.