IAAF president Lord Sebastian Coe has denied allegations he lobbied Lamine Diack to award the 2021 World Athletics Championships to Eugene.
Emails have emerged suggesting Coe "reached out" to former IAAF president Diack before the event was handed to Eugene without a vote, despite interest from Swedish city Gothenburg.
Eugene is situated in Oregon - the state closely associated with American sports corporation Nike. Coe is a Nike ambassador but has denied the allegations and insisted all of his interests are a matter of public record.
"I did not lobby anyone on behalf of the Eugene 2021 bid," said Coe. "After their narrow defeat for the 2019 world championships I encouraged them to re-enter another bidding cycle as they had a strong bid.
"All my interests were, and continue to be, fully declared to the IAAF Ethics Committee and listed at the House of Lords."
However, Bjorn Eriksson, the leader of Gothenburg's bid and the former head of Interpol, has called for an investigation into the process and Lord Coe's role in the decision.
"I would very much like to hear how could this be explained," said Eriksson. "It is a very good question to Sebastian Coe. What is this?
"It smells and it has to be investigated. That's for the sport, for everybody involved."
In August Diack, who is currently suspended from the IAAF and being investigated over allegations he took payments to cover up widespread doping in Russia, defended the decision to award Eugene the event.
"Blame it on an old president on the eve of his departure who wanted to take this opportunity to give this opportunity to the United States," Diack said after stepping down following 16 years in the role as IAAF president.
Coe is due to appear before the culture, media and sport select committee next week when he will face renewed questions over his Nike links and the Russian doping scandal.
The double Olympic gold medallist insists he is still the right man to lead the IAAF, however Folkestone and Hythe MP Damian Collins recently called for him to sever all ties with Nike in order to continue in his role.
It has also emerged that UK Sport part funded Coe's presidential campaign with £63,000 of public money.
UK sport has defended itself in a statement on Tuesday night: "UK Sport invests into the international relations strategies of our National Governing Bodies to help ensure that the UK is in an influential position to drive good governance, leadership and development in international sport."