World number one Jannik Sinner is "honest to the core" and is an "innocent victim" his coach Darren Cahill said after the Italian was cleared of any wrongdoing despite twice testing positive for a banned substance.

The International Tennis Integrity Agency (ITIA) said on Tuesday that Sinner had provided an in-competition sample at the Indian Wells Masters on March 10 which contained the presence of clostebol at low levels.

A further sample, conducted eight days later out of competition, also tested positive for low levels of the same metabolite.

Sinner had explained that the substance had originated from a spray, containing clostebol, that had been used by a member of his staff to treat a cut finger.

The ITIA accepted the explanation and said the "presence of the substance was not intentional".

Cahill told ESPN in a television interview that the staff member in question was physio Giacomo Naldi who had been provided the over-the-counter spray from physical trainer Umberto Ferrara.

The Australian coach said it was not clear exactly how Naldi had provided the contamination to Sinner but suggested "working on the feet, a massage or whatever it may be".

Cahill said there was no question at all of Sinner seeking to gain advantage through use of a banned substance.

"We're not looking for any sorrow or anything because we're quite thankful that there is no ban attached. But I just want to stress that he's a great kid. He's incredibly professional," he said.

"He's maybe the most professional young man that I've ever had the chance to work with. He would never, ever intentionally do anything. He's just in a situation which is incredibly unfortunate. And the truth came out, exactly what happened. There's no fault, no negligence," he said.

"I feel really bad for him that he has to go through this as well because he doesn't deserve this," he added.

Cahill said that Sinner has struggled since the case emerged in March.

"He's been the one who's suffered through this the most and he's the one that's also had to get out there and play tennis and play tennis tournaments," he said.

"So it's been really, really difficult for him and I take my hat off to him that he's been able to get some of the results that he has but there have been days where you can see that he's physically and emotionally he's been challenged on the court."

Some players, such as Australian Nick Kyrgios has questioned the ITIA's decision to accept the story but Cahill said he was not worried about doubters.

"That's ok, I think everyone is entitled to their opinion, I know this is a hugely sensitive issue for everybody, all coaches, all players, all fans.

"I will just stress again that Jannik is the most professional young man that I've had a chance to work with, he's a good man he's been brought up with by wonderful parents. He's honest to the core you can see that in the way he plays.

"He's in a situation where he's the innocent victim of a situation," he added.

Cahill said he did not expect the case to have a long lasting impact on the public perception of the 23-year-old who will be in the spotlight next week at the US Open in New York.

"I think over time this won't affect his legacy in the game I think people will understand it when you read through the entire statement and what he went through and  how they determined him to have no fault or no negligence," he said.