Surrey and Manchester Originals limited-overs batter Laurie Evans has tested positive for “trace amounts of a banned substance”.
It follows a sample provided in August by the 35-year-old while playing for Originals in The Hundred.
The former Sussex and Warwickshire player said he was “shocked” by the test result.
“I believe passionately in clean sport and I have never taken any banned substances,” he said in a statement.
“I don’t know what caused the positive test but my team and I are investigating how this could have happened and I am doing everything possible to find out.
“Due to the confidentiality of the process, I cannot say anything more at this stage.”
Evans has scored more than 10,000 runs in all formats of the game since his first-class debut in 2007.
In recent years, he has become a white-ball specialist, playing in T20 competitions around the world including Australia, Pakistan and the West Indies.
Evans scored 290 runs for Surrey in 15 T20 Blast games last season before playing for Manchester Originals in The Hundred.
A Surrey statement said: “We have been in discussion with Laurie and his representatives and understand he intends to investigate this result.
“We will make no further comment until the process has concluded.”