Grigory Rodchenkov fled to the United States after Moscow issued an arrest warrant

XXIII Olympic Winter Games Venue: Pyeongchang, South Korea Dates: 9-25 February Coverage: Watch live on BBC TV, Red Button, Connected TVs, BBC Sport website and mobile app.

The whistleblower whose evidence led to Russia's ban from next month's Winter Olympics is preparing to testify against those involved - even though his life is under "serious threat", his lawyer says.

Former Russian anti-doping official Grigory Rodchenkov fled to the United States after his allegations about a state-sponsored doping programme.

Russia was banned from the Games after Rodchenkov's claims were investigated - though athletes who can prove they are clean can compete as neutrals.

The International Olympic Committee (IOC) has handed life bans to 43 athletes involved in the doping programme - though 42 of those have appealed to the Court of Arbitration for Sport (Cas).

Their cases will be looked at in the coming weeks and Rodchenkov's lawyer, Jim Walden, says his client will likely give evidence at the hearings.

Walden told BBC Radio 5 live that the threat to Dr Rodchenkov - who was director of Russia's anti-doping laboratory during Sochi 2014 - from Russian retaliation needs to be taken "very seriously".

He added: "We know that Dr Rodchenkov is at the top of the Russian hate list. We know that at least one official has called for Dr Rodchenkov's execution."

But Rodchenkov is still preparing to at testify at the Cas hearings of the athletes and that of Russia's Deputy Prime Minister and former sports minister Vitaly Mutko, who is also banned for his alleged part in the doping scandal.

"He's very focused on what he needs to do in the next several weeks," Walden said.

"Grigory is expected to testify at both proceedings. He's focused on preparing for that. After he gets through these, it's incumbent upon us to make sure he's safe."

Following previous claims that Rodchenkov also has information about doping in football, Walden told BBC Radio 5 live that Fifa, the sport's world governing body, "is considering whether to hire an independent investigator" to look into claims Russia's alleged state-sponsored doping programme included football players.

Russia is hosting the World Cup this summer - though Mutko recently stood down from the tournament's organising committee to focus on contesting his ban.

'IOC chief should resign'

Also speaking to BBC Radio 5 live, Bryan Fogel - the film-maker whose Oscar-nominated Netflix documentary Icarus also helped to expose Russia's alleged state-sponsored doping programme - called on IOC president Thomas Bach to resign.

"The damage to the Olympic movement is unfathomable," Fogel said. "We have to start asking ourselves, why are we having these Olympics? What point are these Olympics other than for a lot of people to make a lot of money at the expense of clean athletes?

"When faced with the biggest scandal in Olympic history - a 40-year-scandal that calls into question the entire history of the Olympic Games - how do they act? They act by giving Russia a slap on the wrist.

"The worldwide community should be calling for the resignation of Thomas Bach. The leadership at the IOC is not the leadership the world should be having if these Games are going to continue."

The BBC has requested a response from both the IOC and Fifa.