American swimming legend Michael Phelps has revealed he is doubtful of a "clean field" at next year's Olympic Games in Tokyo.
Phelps is the most decorated Olympian of all time after claiming 23 gold medals, three silver and two bronze in the pool from Athens 2004, Beijing 2008, London 2012 and Rio 2016.
In an interview with CNN, the 35-year-old was asked how clean he thought Tokyo 2020 would be on a scale of one to 10, to which he answered "four of five".
"I can honestly say that throughout my whole entire career, I don't know if I ever competed in a clean field," Phelps said.
"If that's the case, then yeah, I don't think anything's changed.
"I think there's a lot of issues out there and the fact that we're not held on the same playing field is really upsetting."
Phelps claimed no other Olympic athlete had undergone as many doping tests as he had.
"If we're all getting tested like that, great, but I know we're not," he said.
"Until we are, until we're all held on the same level, nothing's going to change."
There have been concerns the COVID-19 pandemic will impact testing in the run-up to Tokyo 2020, postponed to 2021 as a result of the global health crisis.
The Olympics are now scheduled from July 23 to August 8 and will be followed by the Paralympics from August 24 to September 5.
COVID-19 forced a near global shutdown of drugs testing as countries imposed restrictions in an effort to curb the spread of the virus, sparking fears over the effect on anti-doping.
Testing has resumed across the world amid the return of sports events and figures published by the World Anti-Doping Agency (WADA) during its Foundation Board meeting showed the number of samples collected in September was around 80 per cent of the figure recorded for the same month in 2019.
Some areas are struggling to cope with a second wave of coronavirus, however, which has led to the introduction of further restrictions that could impact anti-doping.
WADA director general Olivier Niggli admitted the Japanese Government has raised concern over the impact of the pandemic on testing in the lead-up to Tokyo 2020, but expressed confidence the system will return to full speed in time for the Games.