Serena Williams pulls out of Madrid Open

Serena Williams has pulled out of the Madrid Open, saying she has been battling the flu and is not feeling 100 per cent.

Serena Williams has pulled out of the Madrid Open, saying she has been battling the flu. (AAP)

Serena Williams will not compete in next week's Madrid Open, the WTA Tour's third Premier Mandatory tournament of the season, after coming down with a fever in recent days.

"Unfortunately, I have to withdraw from Madrid because I've been battling the flu and I'm not at 100 per cent. I look forward to returning soon," the American world No.1 said in a statement released by tournament organisers on Friday.

The absence of Williams, a semifinalist last year and champion in 2012 and 2013, makes Poland's Agnieszka Radwanska the top seed at this elite clay-court event.