The Launceston cyclist was forced to withdraw from the Tirreno-Adriatico yesterday, despite sitting fourth with more climbing and a time trial to come.

The 29-year-old fell ill overnight and his Sky team said he was too unwell to begin the fifth stage.

``We expect him to recover quickly and hope to have him back in training within the next 48 hours,'' team doctor Allan Farrell said.

The enforced withdrawal is a blow to Porte, who had been a late call-up to the race and was optimistic of his chances.

Sky switched him from the planned defence of his Paris-Nice crown when reigning Tour de France champion Chris Froome withdrew with a back injury.

The team's hat-trick of misfortune saw Porte's replacement in France, Brit Geraint Thomas, also forced to drop out following a crash when sitting second overall.

Porte's withdrawal should not affect his longer-term goal of leading Sky in the Giro d'Italia in May.

He will resume racing in support of Froome at the Volta a Catalunya next Monday, which represents the first time Froome and Bradley Wiggins have ridden together since the world championships last season. 

Farrell said Porte could see the bigger picture ahead of the grand tours of Italy and France.

``He's really disappointed but recognises that this is the best course of action to prepare him for his upcoming races. He's looking forward to the Tour of Catalunya next week.''

In the absence of Porte, his former Saxobank teammate and two-time Tour de France winner Alberto Contador won his second successive Tirreno-Adriatico stage to claim the overall lead by 2 minutes and 8 seconds.

Fellow Australian Cadel Evans (BMC) also struggled in the mountains of central Italy, finishing almost 17 minutes behind Contador, but also with one eye on the Giro. 

BMC director Valerio Piva said: ``He needs to refocus on the next stage races, and then he needs to build his condition for the Giro.'' 

Meanwhile, in the Tour of Taiwan, Tasmanians Cameron Wurf and Wes Sulzberger both achieved top ten finishes.

 Cannondale rider Wurf, of Hobart, finished eighth, 15 seconds behind French winner R?aacémy Di Gregorio, and Sulzberger, of Flowery Gully, was tenth for Drapac a second further back.