The World Anti-Doping Agency says the Covid-19 pandemic may have harmed the fight for clean sport and that "additional targeted testing" was being planned to eliminate gaps as competition resumes.

Athletes have expressed concern about reductions in testing for banned substances and urged clarity from authorities about the validity of test results during the global sports shutdown.

WADA, in a questions and answers document for athletes posted on its website late on Monday, said it was monitoring closely where levels of testing had been reduced altogether.

It also said it was in close contact with anti-doping organisations to find the best ways of being effective during this period.

"When the sporting landscape returns to a certain normality, these 'gaps' in testing will be addressed cooperatively through additional targeted testing especially given that intelligence-gathering and investigations continue," WADA said.

"Placing public health above the needs of the anti-doping system means that there may be impacts on the fight against doping in sport.

"However, there is significantly less training being carried out and significantly fewer competitions taking place."

WADA said doping control samples continued to be stored for future analysis and, with the help of the athlete biological passport, some samples collected post-Covid-19 might reveal doping that occurred during the shutdown period.

"WADA is also evaluating what has worked well and what has proved challenging for anti-doping in these unprecedented times," the agency added.

"To that end, WADA is establishing a 'strategic testing' working group in order to learn from this experience and see how the anti-doping system may be strengthened further by this experience."