Simona Halep's former coach Darren Cahill has jumped to the Romanian's defence after the former Wimbledon and French Open champion failed a drug test.

Cahill said Halep's "integrity is faultless" and insisted there was "no chance" she would have deliberately or wittingly taken a banned substance.

It was made public on Friday that 31-year-old Halep tested positive for roxadustat while competing at the US Open in August.

Halep, who has been provisionally suspended, said she felt "confused and betrayed" by the news. She has not explained why, or by whom, she senses a betrayal.

She now risks a ban from tennis and faces a battle to clear her name, which she has said she is determined to achieve.

Cahill was Halep's coach when she landed her first grand slam title at Roland Garros in 2018, and he pointed to his experience of an athlete who was meticulous about checking anything she ingested.

He wrote in a statement posted on Instagram: "Firstly, and most importantly, there is NO chance Simona knowingly or purposely took any substance on the banned list. None. Zero.

"She is an athlete that stressed about anything prescribed to her by a medical professional [which was rarely], or about any supplement that she used or considered. Simona wore out the words 'please double check this, triple check this to make sure it’s legal, safe and permitted. If you are not sure, I'm not taking it.'"

Australian Cahill has also worked with players including Lleyton Hewitt, Ana Ivanovic, Andy Murray and Andre Agassi. He rates Halep as a player and person of the highest order.

When they stopped working together in September 2021, Halep thanked Cahill "for making me a better tennis player and a better person".

Cahill wrote on Sunday: "Simona's integrity is faultless, she respects her peers, she loves the game and she always has her feet firmly planted on the ground as a humble, approachable champion.

"Honesty has always been her greatest strength and her biggest weakness. We would often laugh about the fact that she can't act and can't tell a little white lie.

"She wears her mood on her shoulder for the world to see, for good and for bad. That is Simo. What you see is what you get. She built an amazing career and legacy by doing things the hard way. The right way.

"Due process will now follow to reveal answers to many questions. As Simona said, the hardest match of her life starts now. I believe in her. I always have and can honestly say never more than right now on this particular issue. I stand with Simo."