Williams lost the number one ranking spot to Dinara Safina
World number two Serena Williams has blasted the WTA Tour over its policy for dealing with players who pull out of tournaments through injury.
Williams claimed that players would be fined for pulling out of a tournament even if they were dead.
The outburst came after an injured Williams felt it necessary to play at the Andalucia Tennis Championships.
"It doesn't matter if you're injured, dead or alive, if you don't play they will fine you heavily," she said.
"So I have to play whether I am injured or not. That's just how it is so I have no choice."
Williams suffered a shock first-round defeat to Klara Zakopalova of the Czech Republic in the first round in Marbella.
The American had suffered a thigh strain in the final of the Sony Ericsson Open in Miami the previous week and lost to Belarussian teenager Victoria Azarenka.
Top 10 players must still compete in at least 10 of the 20 Premier events, the four grand slams as well as events at Indian Wells, Miami, Madrid and Beijing.