The illness that has been troubling Oscar Freire since the end of the Tour has forced him out of thePIC BY TDWSPORT.COM Oscar Freire has pulled out of Rabobank's team for the Vuelta after being troubled by headaches and dizzy spells since the final week of the Tour de France. The Spaniard has been replaced by Australia's William Walker, the silver medallist in the under-23 world road race last year, who has been riding for Rabobank's continental team. Freire, who was hoping to use the Vuelta as preparation for a push towards a record-breaking fourth world road race title next month, is due to have extensive neurological examinations. He has already been prescribed tablets to deal with the condition, and had said he was much improved in recent days. However, the Spaniard has since revealed the medication has been making him drowsy, and complicating his training. Walker, who has spoken of his desire to win the Tour one day, is likely to spend most of his time working for defending Vuelta champion Denis Menchov. The Russian, who was handed the title after Roberto Heras was disqualified for doping last year, admits he is not as fresh as he was in 2005 after a tough Tour de France. "I will do the best I can, but I am not making this a clear objective," he says in today's Marca. "I had a bit of bronchitis in the last week of the Tour, and perhaps I also lacked a bit of experience," says Menchov, who finished sixth overall and won a stage in the Pyrenees. Menchov picks out Alejandro Valverde, Carlos Sastre, Alexandre Vinokourov and Iban Mayo as his favourites.