Federer questions inconsistency in Sinner doping case

Swiss tennis great Roger Federer claims anti-doping authorities have questions to answer about a perceived double standard applied to World No.1 Jannik Sinner after the Italian dodged a suspension, despite two positive tests earlier this year.

The 20-time Grand Slam champion called the drama surrounding Italy's Sinner "a tricky situation" and "the nightmare of every athlete", but said he trusts that Sinner did not intentionally use the banned substance clostebol.

"It's not something we want to see in our sport. This type of news, regardless of whether he did something or not ... It's just noise that we don't want," Federer said in an interview with NBC's Today show on Tuesday to promote his new book.

"I understand the frustration about has he been treated the same as others, and I think this is where it comes down to," he said.

"I think we all trust pretty much that Jannik didn't do anything, but the inconsistency potentially that he'd have to sit out while they were not 100 per cent sure about what was going on, I think that's the question here that needs to be answered."

"But it is what it is. We have to trust the process as well of everyone involved."

Sinner has been able to put the controversy aside to reach the US Open quarter-finals, where he meets fifth-seed Daniil Medvedev on Wednesday.