The International Cycling Union (UCI) is investigating after Chris Froome expressed his disappointment at a lack of drug testing at the Tenerife training camp he has been on.
Froome, Great Britain's reigning Tour de France champion who is preparing for this year's race, wrote on his official Twitter account on Wednesday: "Three major TDF contenders staying on Mount Teide and no out of competition tests for the past two weeks. Very disappointing.
"To clarify, I am one of those three and I think it's in all our best interests to be able to prove we are clean no matter where we train."
The 29-year-old Team Sky man was subsequently quoted by Cycling News, where he made it clear the other riders he was referring to were Spain's Alberto Contador (Tinkoff Saxo) and Italian Vincenzo Nibali (Astana), adding: "If we're not getting tested that doesn't look good on any of us."
On Thursday, the UCI responded by saying: "The UCI has seen the comment by Tour de France winner Chris Froome regarding a lack of out of competition testing at Mount Teide, Tenerife.
"Out of competition testing is clearly an essential component of any effective anti-doping programme and we are looking into the matter with the Cycling Anti Doping Foundation, which is responsible for planning and executing anti-doping tests in cycling."
Contador was stripped of his 2010 Tour de France victory after testing positive for clenbuterol, after which he was handed a two-year ban back-dated to January 2011.
In his Cycling News quotes, Froome said: "I've asked around with other teams just out of interest, because we've been up here before and not been tested, so I just wanted to see if it was the same case for everyone but none of them, from what I could gather, had been tested either.
"Alberto, Vincenzo, we're all up here with our respective teams and at the end of the day we're the ones that have to stand in front of the television cameras in July and justify performances.
"All three of us are GC (general classification) contenders and the probability is that whoever is in the yellow jersey in July is going to have to answer questions and if we're not getting tested that doesn't look good on any of us."
He added: "We're doing everything we can to show that cycling has turned a page and it's not like it was in the past, but things like this don't help.
"I know from last year, journalists do ask whether we've been tested while we've been up here and we can only say we weren't. That's not good for the image of the sport or peace of mind.
"It would be good to have more testing done up here, especially this close to the Tour de France.
"I've been tested once and I've been up here maybe four or five times.
"We're all in the same hotel and we're all just a few doors away from each other. We have dinner together and at the end of the day the anti-doping authorities aren't the ones who have to stand in front of the media in July and justify the sport.
"In my opinion they're not helping by not doing controls at this part in the season."