The reduced amount of testing during the coronavirus pandemic will give athletes a 'window of opportunity' to cheat the system, says the head of the US Anti-Doping Agency Travis Tygart.

More than a quarter of the world is now in lockdown as a result of the virus, meaning it is difficult for organisations such as USADA to carry out as many tests as they usually would.

And while Tygart feels the postponed Tokyo Olympics could be 'the cleanest games we've seen', he is aware over this period there will be some athletes who attempt to use it as a chance to cheat the system.

Speaking to BBC Sport, he said: "I think clean athletes are going to compete clean and are not going to try and take advantage of this situation.

"What we worry about is those who otherwise may not be willing to compete clean and will try everything to get away with it. It does for a period of time at least open that window of opportunity."