The decision by the scandal-hit IAAF to award the 2021 World Athletics Championships to the American city of Eugene is being investigated by French prosecutors, the BBC has learned.
Eugene, closely linked to sportswear giant Nike, was given the event without the usual bidding process.
French officials are investigating corruption allegations involving former IAAF president Lamine Diack already.
And they have launched a fresh inquiry into how Eugene won the 2021 event.
Last month, current IAAF president Lord Coe severed his links to Nike two days after a BBC story suggested he had held talks with Diack and Nike about the awarding of the 2021 event while he was on the Nike payroll.
Lord Coe said at the time that he "did not lobby anyone" over Eugene's bid, but simply "encouraged them to re-enter another bidding cycle as they had a strong bid".
An email, dated 30 January 2015, from Nike executive Craig Masback to Vin Linnana, head of Eugene's bid, was sent after Masback held talks with Lord Coe.
During that meeting Lord Coe apparently "made clear his support for 2021 in Eugene but made equally clear he had reached out to Diack specifically on this topic and got a clear statement from Diack that 'I am not going to take any action at the April meeting [in Beijing] to choose a 2021 site'."
However, at that April meeting of the IAAF's council Diack announced a surprise vote on giving the championships directly to Eugene. It went through 23-1 with one abstention, with Lord Coe voting in favour.
Other emails seen by the BBC reveal that Lananna made at least one trip to Europe to visit Diack a few weeks after this email was written.
BBC sources have confirmed French investigators want to know more about how Diack arrived at the decision to give Eugene the event.
French police, instructed by lead financial prosecutor Elaine Houlette, have already arrested and questioned Lamine Diack, his legal adviser Habib Cisse and Gabriel Dolle, the former long-standing head of the IAAF's anti-doping unit.
Diack's son, Papa Massata, is also wanted for questioning but is believed to be in his native Senegal.
Houlette has previously said that Lamine Diack allegedly pocketed more than £1m euros as part of a scheme to cover up suspected Russian athletes' doping.
Lord Coe, who was a vice president of the IAAF under Lamine Diack for seven years, has been questioned voluntarily by French police.
He told the BBC he supported Eugene because it presented a "unique financial and political opportunity" that may not arise again.
He denied his conversation with Masback was a conflict of interest between his then roles as vice-president of the IAAF and his ambassadorial role at Nike, which was worth a reported £100,000-a-year.
Coe said he was unaware of Diack's decision to hand the event to Eugene without a bidding process until a few days before the April vote was called.
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Eugene is the birthplace of and synonymous with Nike, which could stand to benefit financially from the event.
Two days after the email was published by the BBC, Lord Coe - albeit reluctantly - announced he was ending his 38-year ambassadorial role at Nike, despite the IAAF ethics committee telling him he was welcome to keep the role.
Speaking at a news conference in Monaco following an IAAF council meeting, Coe said of his Nike role: "The current noise level around it is not good for Nike or the IAAF."
Lord Coe, who was grilled by MPs last week over his links to Nike and his role at the IAAF, has stated that he was unaware of any corrupt practices at the IAAF.
The move to award the event to Eugene led to criticism from Swedish city of Gothenburg, which was planning to bid.
Leader of the Gothenburg bid at the time and former head of Interpol, Bjorn Eriksson, told the BBC that the conflict of interest allegations about Lord Coe needed "an explanation".
Meanwhile, the IAAF ethics commission is to hold a session next week in London over the corruption allegations.
A panel of the commission, comprising Thomas Murray and Akira Kawamura and chaired by Michael Beloff QC, is due to hear evidence concerning the IAAF ethics code charges it has issued against Papa Massata Diack, a former consultant to the IAAF; Valentin Balakhnichev, former president of the All-Russia Athletic Federation (ARAF); Alexei Melnikov, former chief ARAF coach for long distance walkers and runners; and Gabriel Dolle, former director of the IAAF's Anti-Doping Department.
One of the ethics commission members who signed off on the ethics charges laid against the four has previously faced corruption claims.
Kevan Gosper, a former vice-president of the International Olympic Committee, faced corruption allegations relating to the notorious Salt Lake City Winter Olympics when the bidding city paid for two trips to Utah for Gosper and his family.
He resigned in 2000 from the IOC's ethics committee over the claims - made by the journalist Andrew Jennings - but was cleared of any wrongdoing by the committee, which concluded he had not knowingly or negligently violated IOC rules.
Another member of the IAAF ethics commission - which gave Lord Coe the all-clear to continue his association with Nike - is the Brazilian Carlos Nuzman, president of the Rio Olympics 2016 organising committee.
In 2012, he helped land a major Nike sponsorship deal for the Brazilian Olympic Committee.
At the time, he said: "Brazil is one of the most sport-obsessed nations on earth and Nike and Brazil have the same DNA in sport. Now we'll be able to work together in a partnership that will certainly be significant for both partners."
Current investigations into athletics
World Anti-Doping Agency (Wada)
Following its report into systematic doping in Russian athletics, Wada is expected to publish the second part of its report focusing on possible corruption within the IAAF early next year.
French financial prosecutors
French prosecutors are investigating former IAAF president Lamine Diack and three others over allegations of corruption, bribery and covering up suspicious dope tests.
IAAF ethics commission
Four IAAF officials, including Lamine Diack's son Papa Massata Diack, have been charged with various alleged breaches of the governing body's code of conduct and will have their cases heard in front of an IAAF ethics commission panel next week.
US Anti-Doping Agency (Usada)
Usada is currently investigating doping allegations against Nike Oregon Project coach Alberto Salazar following a BBC Panorama documentary in June.
Additional reporting: Calum McKay