Baku, January 25, AZERTAC
Adidas, the IAAF's biggest sponsor, has told athletics' world governing body it is to terminate their sponsorship deal four years early, according to BBC.
The sportswear giant informed the IAAF of its decision - understood to be a direct result of the doping scandal sweeping the sport - last week.
Sources say the move will cost the IAAF and its commercial partner Dentsu tens of millions of dollars in revenue.
It is sure to come as a major blow for embattled president Lord Coe.
Neither Adidas nor the IAAF - the International Association of Athletics Federations - confirmed the split but both issued short statements.
They both referenced the "reform process" currently under way as the IAAF attempts to come to terms with a number of damaging revelations.
They also claimed they were "in close contact" with each other, with the IAAF insisting it was in close contact with "all its sponsors and partners".
Adidas, which designs and manufactures sports shoes, clothing and accessories, has also expressed its displeasure at the corruption scandal that continues to engulf FIFA.
However, the German firm, which signed a £750m kit sponsorship deal with British football giants Manchester United in 2014, remains world football's governing body's oldest commercial partner.
The 11-year sponsorship deal with Adidas was due to run until 2019 and was reportedly worth $33m (£23m).