The IAAF has opened an investigation into whether the winner of the 2016 Jersey Marathon was ineligible to race because of the ban on Russian athletes.
Aleksey Troshkin won the event for the third straight year earlier this month, just outside his own course record.
But, following allegations of state-sponsored doping, the IAAF had banned all Russian athletes from competing outside of their homeland.
Troshkin may lose the title if he is found to have breached the ban.
An International Association of Athletics Federations spokesman told BBC Sport: "We are investigating now. We have asked the organisers to send the full information we need."
While there is no suggestion Troshkin has taken performance-enhancing drugs, if he was ineligible he will be stripped of the title, meaning American runner-up Chris Zablocki would be declared the winner.
Race organisers 3D Events said in a statement: "We are aware of the speculation surrounding the Jersey Marathon 2016 male winner Aleksey Troshkin and are currently awaiting for an official ruling from the IAAF as they consider his case.
"We are working with UK Athletics and the IAAF and will provide an updated statement once we have further information."