Former world number one Simona Halep said Friday she will “fight until the end” to prove she did not knowingly take a prohibited substance after she was provisionally suspended for doping.

A sample that Halep provided during the US Open in August showed traces of Roxadustat, a drug that stimulates the production of red blood cells and is used in the treatment of patients with kidney problems, the International Tennis Integrity Agency (ITIA) said.

Halep, the current world number nine, said the positive test was “the biggest shock of my life”.

“Throughout my whole career, the idea of cheating never even crossed my mind once, as it is totally against all the values I have been educated with,” the Romanian tweeted.

The 31-year-old said an “extremely low quantity” of the substance had been found in her body.

“I will fight until the end to prove that I never knowingly took any prohibited substance and I have faith that sooner or later, the truth will come out,” Halep added.

The 2018 French Open and 2019 Wimbledon champion had ended her season in mid-September after having nose surgery.

She said that in February she had considered ending her career but she began working with Serena Williams’ former coach Patrick Mouratoglou and her form briefly rebounded.

She reached the semi-finals at Wimbledon this year and won in Toronto to reach No.6 in the rankings in August before slipping back to ninth.

The ITIA, which oversees tennis’ anti-doping programme, said it had informed her on October 7 that she was being provisionally suspended.