The credit ratings of Clear Channel Communications and CC Media, its private equity-controlled holding company, were cut on Monday by Standard & Poor’s, amid uncertainty about the US radio and outdoor advertising group’s ability to avoid defaulting on its $20bn of debt.

If senior secured lenders refused a proposed debt exchange, “we are concerned that it could violate financial covenants and would be unable to absorb a potential interest rate increase that could accompany an amendment, forcing it into bankruptcy,” the agency warned.