CNN)Michael Phelps, who retired as the most decorated Olympian in history in 2016, is not holding out much hope for a clean Olympics Games in Tokyo next year.
Asked how clean he thinks the Games will be the 23-time Olympic gold medalist bluntly told CNN Sport's Don Riddell: "Four or five" out of 10.
"I can honestly say that throughout my whole entire career, I don't know if I ever competed in a clean field," added Phelps.
"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."
This year marked the eight-year-anniversary of the 2012 Olympics in London, where Phelps won four gold medals.
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Those Games have been described as the dirtiest Olympics in history, with more than 130 athletes banned or disqualified for doping offenses, according to Olympedia.
68 of those athletes were found via a re-analysis program that continues to re-test samples from previous Olympic Games.
Meanwhile, according to a New York Times report, of approximately 11,000 athletes who competed at the 2016 Rio Olympics, about one out of every 100 competitor had served suspensions or had to return medals because of doping.
Phelps, who was outspoken on drug cheats throughout his career, says he can "guarantee" no athlete has been tested as much as he was on an Olympic level and insists everyone should be held to the same high standards.
"If we're all getting tested like that, great, but I know we're not," added the 35-year-old. "Until we are, until we're all held on the same level, nothing's going to change."
The International Olympic Committee (IOC), which oversees the drug testing at the Games, has maintained that fighting for clean sport is among its top priorities.
CNN reached out to the World Anti-Doping Agency which referred it to the IOC.
In response to CNN's request for comment, the IOC stressed a number of anti-doping measures that the organization had introduced, notably the work of an expert group, led by the International Testing Agency (ITA), to close testing gaps ahead of the Games.
It also said the Olympic Movement spends $260 million every four years to fight against doping, with $136 million coming from the IOC directly.