Vauxhall MasterFit have decided not to renew their two-year sponsorship of the Welsh Premier. Officials had hoped the car maker would continue the association, worth �50,000 a year, split between all the clubs.
The decision leaves the league with less than eight weeks to find a new backer for the competition.
"The Vauxhall MasterFit partnership was the most successful commercial deal since the launch of the Welsh Premier," said league secretary John Deakin.
"The sponsor has benefited from unrivalled brand positioning opportunities by partnering with the league for a sustained period."
The company was the third sponsor in the 14-year history of the league, following Konica Peter Llewellyn Limited of Swansea and car dealer JT Hughes Mitsubishi.
It is understood that the league's clubs rejected an approach from a major building society last year in order to continue with Vauxhall MasterFit.