Serena Williams on Sunday blamed physical exhaustion for her withdrawal from the US team to face Italy in the Fed Cup final.
The world number one had been called up for the first time since 2007 to lead the American challenge in Reggio Calabria from November 7-8, but she insisted that her body would not hold up.
"I definitely really want to go, but I don't think I would do well physically," said Serena after defeating sister Venus in the WTA Championships final here on Sunday.
"It's very difficult to play such a mental week and then come back and play again. Right now I'm just struggling in every aspect of my body.
"It's a very difficult decision that I actually couldn't make. I had to get input from my mom and my dad. People that are close to me had to just basically tell me what I needed to do as opposed to me making the decision."
The US team to tackle Italy will be made up of Vania King, Alexa Glatch, US Open quarter-finalist Melanie Oudin and doubles specialist Liezel Huber.
