Doping probe hits Russian football
All 23 members of country's 2014 World Cup squad are allegedly under investigation
Fifa insists that "it is still investigating allegations" that Russian footballers were involved in a state-sponsored doping programme.
At least 30 sports, including football, covered up samples involving more than 1,000 athletes between 2011 and 2015, according to the McLaren report.
A Sunday newspaper revealed that Fifa was investigating if Russia's 2014 World Cup squad were part of the programme. All of their players are now under examination.
Russia is currently hosting the Confederations Cup and in under a year will stage the World Cup but these allegations are likely to throw its suitability to stage such events into serious doubt.
Five of the players from the 2014 squad - Igor Akinfeev, Denis Glushakov, Maksim Kanunnikov, Aleksandr Samedov and Yuri Zhirkov - are in the current team, which was eliminated on Saturday following their 2-1 defeat by Mexico.
Fifa insists that no players from the 2014 World Cup returned a positive test, while Russia's deputy prime minister Vitaly Mutko, who is also head of the Russian Football Union, dismissed the allegations and said there never was nor will be doping in Russian soccer.
"Don't pay attention to this, they have been writing about us negatively since 2010," Mutko said.
"Our national team is endlessly checked. We have doping tests at all matches. In soccer this has never been a central theme."
Fifa said it had not referred to any particular players and "cannot comment on the status of ongoing investigations".
It said it wanted investigations to be completed quickly and that it could not provide further details until then.
"Fifa has simply confirmed that, in close collaboration with Wada (World Anti-Doping Agency) it is still investigating the allegations involving football players in the so-called McLaren report," a Fifa spokesman said.
"However, Fifa did not refer to any particular players, since it cannot comment on the status of ongoing investigations."
The McLaren report alleged that Russian authorities assisted athletes taking banned drugs by swapping their positive samples for clean ones.
But Fifa said that samples taken from players at the 2014 World Cup, including the full Russian squad, were sent to a Wada-accredited laboratory in Lausanne, Switzerland.
"As far as the Fifa Confederations Cup is concerned, every participating player has been tested through blood and urine in unannounced controls," Fifa added.
"Both the results of the unannounced and the post-match tests have been negative so far."
Russia were knocked out in the group stage of the tournament after losing to Belgium and drawing against South Korea and Algeria.
Professor Richard McLaren confirmed that 33 football players, including some foreigners, were listed in his report, although no other details were revealed with information passed on to federations and regulatory bodies.
The report comes after FIFA replaced its top two ethics officials without warning at its annual congress last month in Bahrain.
Former WADA chief Dick Pound told the Mail on Sunday: "There is a huge onus on FIFA to reach a sensible conclusion on these matters before the World Cup takes place.
"It is incumbent on them to say what steps they are taking, what they find, and take whatever action necessary to protect the integrity of sport.
"Even within a governing body with as little credibility remaining as FIFA, if you were a senior official you wouldn't want to be part of a body that ignores this.
"There has been an institutional denial of doping in football for years.
"I've seen too many presentations by FIFA, straight out of fantasy land, about how they don't have a problem.
"They absolutely have to take this case seriously."