UEFA has criticised the World Anti-Doping Agency (WADA) after Liverpool defender Mamadou Sakho was briefly suspended following a drug test last year.
UEFA suspended Sakho for 30 days in April 2016 after an alleged anti-doping violation following Liverpool's Europa League match against Manchester United in March, which resulted in him missing the run-in -- including the club's Europa League final defeat to Sevilla -- as well as losing out on a place in France's Euro 2016 squad.
Sakho, who joined Crystal Palace on loan in January, had tested positive for higenamine -- a chemical compound predominantly used in fat-burning substances that was thought to be on WADA's Prohibited List -- after a sample was sent to a WADA laboratory in Cologne.
However, it was reported in the aftermath of the suspension that UEFA was investigating whether higenamine should have been on the list, and in July last year he was cleared by a UEFA board.
European football's governing body has now expressed frustration over the matter, saying the test for higenamine would not even have taken place had the sample been sent to WADA's laboratory in Lausanne.
A report into the case by UEFA's Controls, Ethics and Disciplinary Body read: "It is clearly not possible for anyone, laboratory disciplinary body, football player or otherwise, to know whether or not higenamine is a prohibited substance by reading WADA's prohibited list.
"The fact that the Cologne laboratory tested for higenamine but had to check with WADA before making a determination indicates a problem, as does the fact that the Lausanne laboratory does not test for it.
"The onus is clearly on WADA to communicate to its laboratories what is and what is not on the prohibited list."
WADA spokesman Ben Nichols said in The Guardian that UEFA's criticism was unfair as his organisation had "supported the List Expert Group's unanimous view that higenamine is a beta2-agonist and does indeed fall within the S3 class of the Prohibited List" during the Sakho case.
He said WADA had decided not to lodge an appeal "after careful review of the specific circumstances of the case."
Explaining the discrepancy in which of its laboratories tested for the substance at the time the Sakho sample was submitted, he said: "Whilst higenamine has been considered prohibited since 2004, its prevalence within dietary supplements has surfaced more recently.
"Therefore, in early August 2016, WADA requested its network of accredited laboratories to implement systematic testing for higenamine; although, it is clear that some laboratories already conducted routine testing for higenamine before this date."
Sakho has not played for Liverpool since the suspension, with Jurgen Klopp having sent him home from a preseason tour in the United States last summer for unrelated breaches of club rules.
Klopp has remained coy on whether Sakho could have a future at Liverpool once his loan at Palace expires.