Clément Lhotellerie (Skil-Shimano) is rumoured to be one of the 23 riders who "warranted further scrutiny" as part of the UCI's blood passport scheme.
The Frenchman won the mountains jersey in Paris-Nice but has been out of action since then because of a knee injury. He returned this week for the Four Days of Dunkirk, placing second in the first stage and is currently lying in second overall.
But Dutch newspaper Algemeen Dagblad wrote that his knee injury was a "classic excuse" to avoid falling foul of the anti-doping authorities. The paper anonymously quoted a teammate as saying that Lhotellerie was putting the Skil-Shimano team in danger because of his "shady practices".
Skil-Shimano management say they don't know whether Lhotellerie is one of the 23 riders on the UCI's question mark list.
"Really, I can't say anything," said team manager Iwan Spekenbrink to AD. "I'm not aware of any manipulation through one of our riders, let alone been informed or warned by the UCI that someone has been manipulating [themselves]."
In comments to AFP, Lhotellerie denied that he was one of the riders targeted by the UCI, reiterating that the reason he had missed the spring classics was because of a knee injury.