The $19.5bn leveraged buy-out of Clear Channel Communications (NYSE: CCU - News) , the US radio and outdoor advertising group, could be the next victim of the storm in the deal world.

Scepticism that Thomas H. Lee and Bain Capital will go through with their purchase on the original terms has been fed by the falling share prices of comparable companies.

Clear Channel's stock traded on Monday at $35.06, a discount to the $39.20 price the buyers agreed in May 2007, which suggests that investors are betting against the deal.

The concerns are surfacing in the wake of last week's collapse of an agreement by General Electric (NYSE: GE - News) and Blackstone to buy PHH, a mortgage and vehicle leasing company. Unlike PHH, Clear Channel is hardly a sick company, which suggests that concerns about the overall economy are now threatening a wider range of leveraged buy-outs.

"It is susceptible to recession but that was built into the plan," said one person familiar with the thinking of the buying group. "There is no good reason to walk."

The purchase is expected to receive FCC approval as early as the end of this week. Bankers familiar with the transaction say the buyers are unlikely to do anything before regulators sign off on the deal, if only to keep their options open.

"I don't see anything yet that indicates the deal won't go through," said one senior banker involved in the deal. "But there are a lot of undercurrents, including the fact that the returns for the sponsors are terrible and the break-up fee isn't huge."

If the private equity buyers walk away, they would be likely to have to pay a $500m break-up fee to the company.

Some of the banks providing the debt are also committed to coming up with some of the equity and would share in paying that fee. Banks have been trying to reduce financing commitments for buy-outs.

Even when the deal was first struck, in November 2006, competitors to Thomas H Lee and Bain Capital thought the terms aggressive.

Radio broadcasters have seen their revenue growth stall and their growth prospects fade in the face of fresh competition from internet and satellite radio companies and the popularity of Apple's iPod.