Frank Schleck visited a Pau police station after leaving the Tour de France following a positive drugs test, his RadioShack-Nissan-Trek team confirmed.
The 32-year-old Luxembourg rider, who finished third in the 2011 Tour, tested positive for banned diuretic Xipamide on July 14, cycling's world governing body, the Union Cycliste Internationale announced.
Schleck will not start Wednesday's 16th stage, the 197-kilometre route from Pau to Bagneres-de-Luchon, but RadioShack-Nissan-Trek will remain in the Tour.
Schleck was 12th overall, nine minutes and 45 seconds behind leader Bradley Wiggins (Team Sky), at Tuesday's second rest day and has the right to attend the analysis of his B sample within four days.
RadioShack-Nissan-Trek spokesman Philippe Maertens confirmed Schleck had voluntarily gone to the French police on receipt of the news for questioning. Maertens said Schleck had gone to the police station because he knew the authorities would be seeking to speak to him.
There were uniformed and plain clothes officers at the hotel, but Maertens insisted rooms had not been searched. He said: "He tested positive for Xipamide. It's not a performance-enhancing product, but it's forbidden. The team doesn't know where that product comes from.
"RadioShack will stay in the Tour. He's not suspended. Even the UCI cannot say to him 'you have to go'."
Asked Schleck's reaction to the news, Maertens said: "It was like he got a hammer on his head. He doesn't know anything about where the product comes from.
"It's a shock for everybody. We're having a good Tour de France. We're leading the team classification, it's a big goal for us.
"Without Frank Schleck it's going to be harder. All our riders are working for one goal. When something happens like this you can imagine they are not happy."