The world number one was cleared of wrongdoing last month after it was revealed that a small trace of the banned anabolic steroid clostebol was found in his system in March.

Sinner was let off after explaining that the substance entered his body after a massage from his physio who had used a medical spray to treat a cut on his finger but Federer doesn't think he should have been allowed to continue competing.

The retired tennis legend told 'Today': "I understand the frustration of, ‘Has he been treated the same as others?' And I think this is where it comes down to.

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

Federer thinks that Sinner's case has damaged the reputation of tennis but accepts that the matter is complex for the sport's authorities to deal with.

The 20-time Grand Slam winner said: "It’s not something we want to see in our sport — this type of news — regardless if he did something or not, or any player did. It’s just noise that we don’t want.

"I understand it’s a tricky situation. It’s the nightmare of every athlete and team to have these allegations and these problems because we fill out these forms all day, every day.

"And it lives with you. Every morning when you wake up, you think, ‘Is somebody at the door coming to test me?’ So it’s really difficult."