Simona Halep's former coach Darren Cahill said there is "no chance" the two-times Grand Slam champion had knowingly taken a prohibited substance after she was provisionally suspended for failing a drug test.
Halep, ranked ninth in the world, was tested during the U.S. Open and both her A and B samples confirmed the presence of roxadustat, the International Tennis Integrity Agency (ITIA) said on Friday.
Cahill, who worked with Halep for six years and guided her to her first Grand Slam title - the 2018 French Open - said the Romanian's integrity was "faultless".
"Firstly, and most importantly, there is NO chance Simona knowingly or purposely took any substance on the banned list. None. Zero," Cahill wrote in a post on Instagram.
"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 ...
"We both believe in the ITIA testing program and would often discuss the number of times she was tested, both at tournaments and randomly. She did it without complaint, with the reassurance of knowing other athletes were being tested just as frequently."
Former world number one Halep, who also won Wimbledon in 2019, described the ban as the "biggest shock of her life" and denied knowingly taking any banned substance.
"Due process will now follow to reveal answers to many questions. As Simona said, the hardest match of her life starts now," Cahill added.
"I believe in her. I always have and can honestly say never more than right now on this particular issue."
Halep's suspension means that she cannot compete in or attend any sanctioned events organised by the governing bodies of tennis.