The pair were tested by the Pakistan Cricket Board [PCB] as part of its requirements prior to the tournament in India and showed positive results for the anabolic steroid nandrolone.

A statement from the PCB read: "The PCB has asked for reconfirmation of the tests from the Malaysian laboratory and the results are expected by tomorrow. PCB has decided to withdraw the two players from the ICC Champions Trophy 2006 immediately. The players will return back home on the first available flight."

Shoaib and Asif have recently recovered from serious injuries and only returned to action towards the end of Pakistan's recent tour of England. Shoaib had been troubled for most of the year by knee and ankle problems while Asif was affected by an elbow injury.

Bob Woolmer, the Pakistan coach, believes the players must have taken the substances inadvertently during their rehabilitation. "I very much doubt whether either player would take this particular substance to enhance performance but both have been returning from injuries and I wonder whether the substance found was in the injections for that injury," Woolmer said. "I'm just hoping it is a very accidental thing and I rather think it is."

Shoaib, who has taken 165 Test and 208 one-day international wickets for Pakistan, protested his innocence: "I have done nothing wrong. The president [of the PCB] has asked me not to comment at this stage."

The International Cricket Council [ICC] has signed up to the World Anti-Doping Agency’s code and the players could face hefty bans. Malcolm Speed, the ICC chief executive, told BBC Radio Five Live: "Cricket is generally regarded as a low-risk sport. The risk for cricket would be a player injured taking a substance inadvisedly to come back quickly.

"We take a zero-tolerance approach to drugs. We are disappointed this has happened and disappointed for these players. We will get to the bottom of it."

The most high-profile doping incident in cricket relating to non-recreational drugs concerned Shane Warne, the Australia leg-spinner, in 2003. Warne was banned for a year after testing positive for a diuretic, which can be used as a masking agent for other substances.

The news comes after a turbulent couple of months for Pakistan cricket following the Oval ball-tampering fiasco, board upheaval and the resignation and re-appointment of Younis Khan as stand-in captain.