Pakistan spinner Abdur Rehman tested positive for recreational drugs whilst playing for Somerset this summer.
Rehman was a huge success for Somerset, taking 27 wickets in just four Division One matches after arriving in August, including a career-best 9-65 against Worcestershire.
Rehman insists he is not guilty of taking any prohibited substances.
"I don't know what has happened. I am also in the dark as I don't use medicines or substances," he said.
He is not part of Pakistan's squad at the World Twenty20 but is a key man in their Test and one-day team.
The Pakistan Cricket Board has withdrawn Rehman from the Sialkot Stallions squad due to play in the Champions League Twenty20 qualifying tournament in South Africa starting on October 9.
A PCB spokesman said: "We have withdrawn Rehman's name from the list after the England and Wales cricket board informed us that he had tested positive in a dope test taken in August after a county match."
Overall the left-arm spinner has 81 wickets in 17 Tests at 28.40 apiece and he was a huge thorn in England's side in the winter series in the UAE, taking 19 wickets in three matches.
He could be banned for up to two years if he is found guilty.
Sri Lankan opener Upul Tharanga was banned last year for three months after failing a dope test at the 2011 World Cup.