Chris Froome says questions remain over Team Sky and Sir Bradley Wiggins seeking permission to use anti-inflammatory drug triamcinolone.
Wiggins in 2012 became the first British Tour de France winner and Froome has since inherited the Team Sky leadership and won the yellow jersey three times, in 2013, 2015 and 2016.
Wiggins received three therapeutic use exemptions (TUEs) for triamcinolone -- a substance which has a history of abuse in cycling and is otherwise banned -- on the eve of the 2011 and 2012 Tours and 2013 Giro d'Italia.
Wiggins and Team Sky principal Sir Dave Brailsford have strenuously denied any wrongdoing, insisting each time the TUEs were medically necessary to deal with a pollen allergy that aggravated Wiggins' long-standing asthma condition.
The TUEs also had the approval of the UCI, cycling's world governing body, and there is no suggestion that Wiggins or the team have broken any rules.
Froome, however, was unaware of his former teammate's TUEs, with Wiggins leaving the team in April 2015.
"I was surprised, it was the first that I had heard of them," he told cyclingnews.com. "I had seen Bradley Wiggins using his inhalers so I knew he had asthma, but I wasn't aware of his allergies.
"Without knowing the exact details of his medical condition, it's impossible to say if he was operating in a grey area."
Froome has previously secured two TUEs for short courses of prednisolone, a steroid used to treat acute chest complaints, in 2013 and 2014.
The latter was controversial at the time as it was granted retrospectively to enable the 31-year-old Froome to take part in a key Tour de France warm-up race in Switzerland, despite being ill a week before.
His TUE application was cleared by the UCI and WADA and he went on to win the Tour de Romandie.
Cyclingnews.com said it asked Froome the difference between the TUE cases, with the 31-year-old replying by email, outlining the history of the case.
"This is the standard treatment for post-infection inflammation in asthmatics that cannot be controlled by standard inhalers," Froome added. "I don't believe that there are any alternative treatments, and performance enhancement is negligible.
"With regards to Wiggins' TUEs, questions remain over his symptoms, the choice of treatment and the related performance benefits from that treatment."
While Froome admitted there were questions to answer, former Team Sky rider Mark Cavendish insisted it was unfair to subject Wiggins to speculation about his TUE use without a more detailed explanation of his health condition.
He told the Daily Telegraph: "This is not sticking up for Brad and it's not getting at Brad -- just take away who is involved for the moment -- there are rules. And you either break the rules or you don't break the rules. And unless you know Brad's medical situation, the rest is just speculation.
"Maybe Brad needed a TUE legitimately; maybe he could have used something else. But unless you know, it is just speculation. And I'm not going to speculate."
UCI president Brian Cookson, who was British Cycling president until his election to the world governing body in September 2013 and also sat on the Team Sky board, says Team Sky and Wiggins operated within the rules.
"The issue of the substances issued to Wiggins appears to have been within the rules," Cookson told reporters at the UCI Road World Championships, which concluded in Doha on Sunday. "But I think there is an argument to be had about whether TUEs for that kind of substance are valid."
Since the TUEs leak, UK Anti-Doping has launched an investigation into allegations of "wrongdoing" in cycling.
Froome, who has been on a family holiday in recent weeks, added: "It's a great shame for the sport that we're once again debating the validity of a Tour de France victory, and it has been a very challenging time for those involved.
"Like many other members of the team, I look forward to the conclusion of the investigation that is currently taking place and getting back to focusing on the season ahead."