FIFA has ended a doping investigation into Russian footballers named in the country's provisional World Cup squad after finding "insufficient evidence" of any wrongdoing, it said on Tuesday.
World football's governing body launched a probe into "possible anti-doping rule violations" by players "against whom a suspicion had been raised" following the publication of the McLaren report on mass doping in Russia.
The enquiry was part of a broader investigation into players likely to participate at the World Cup, the result of which was "that insufficient evidence was found to assert an anti-doping rule violation", FIFA said in a statement.
FIFA added it had "informed the World Anti-Doping Agency (WADA) of its conclusions, and WADA in turn has agreed with FIFA's decision to close the cases."
The report by Canadian lawyer Richard McLaren, produced at the request of WADA, revealed a "state-sponsored" doping system in Russia that reached its peak during the 2014 Winter Olympics in Sochi.
The bombshell revelations prompted the suspension of numerous Russian athletes with several stripped of medals, while the country was formally banned from the 2018 Winter Games in Pyeongchang, where Russian competitors were only allowed to take part as 'neutrals'.
Several Russian footballers were named in the McLaren report, although they were never publicly identified.
As part of the probe, FIFA said it carried out "an assessment of all information and evidence contained in the McLaren report, with the support of scientific and legal experts."
FIFA also got in touch with McLaren "to obtain further details from him" and sent questions to Grigory Rodchenkov, the Russian whistleblower who served as the former head of Moscow's anti-doping laboratory.
Samples taken by FIFA and confederations which were stored in WADA-accredited laboratories of players listed in the McLaren report and "high-level" players were re-analysed for banned substances.
Samples seized by WADA from the Moscow laboratory were also retested.
"All results were negative," FIFA said.
In addition, FIFA performed unannounced doping controls during the process of the investigation, with the Russian squad "one of the most tested teams" ahead of the tournament.
FIFA said it was also still working alongside WADA on an investigation into several players who will not be involved at the World Cup.