The entire starting XI of Russian side FC Rostov was subjected to surprise doping tests following their 3-1 victory over Dinamo Moscow on Thursday.
Having finished 14th last season and avoided relegation in the end-of-season play-off, unfancied Rostov have risen to second place during the current campaign and sit two points behind leaders CSKA Moscow.
A FIFA statement quoted by Reuters confirmed the tests were undertaken following media reports of possible use of meldonium, a substance that has been banned by the World Anti-Doping Agency (WADA) since January 1.
"We have today done an unannounced [doping] control of a football club, Rostov," FIFA chief medical officer Jiri Dvorak told the Associated Press at the FIFA Congress in Mexico City.
"We tested the entire team, the 11 who were on the start list. The entire procedure took two hours. It is done and the samples will be tested in one of the accredited laboratories in Europe."
He added: "There were some rumours in the media about meldonium and Rostov ordering meldonium.
"What is true on it I can't really say anything... we are not really following every rumor but [with] the current situation with meldonium we thought it is just a good example just to do it."
Russian athletes are currently facing a ban from the Olympic Games in Rio de Janeiro this summer following a WADA commission that revealed widespread state-sponsored doping.
At least 16 Russian athletes, including tennis star Maria Sharapova, have tested positive for meldonium since it was banned at the start of the year.
Before the ban, meldonium was widely used in Russian sport. Its primary medical function is to treat heart disease but it can have performance-enhancing properties through metabolic modulation.
- Goal