If you own UAL ( UAL) shares, you might want to sell them while you still can. That's what Credit Suisse First Boston analyst James Higgins advised Tuesday in a new research note bluntly titled, "Liquidity Concerns Worsen: Sell UAL Shares." Other Wall Street analysts have been issuing similar advice, as the parent of United Airlines, the second-largest carrier, stumbles toward bankruptcy. UAL was down 4% at $3.15 following the CSFB note. UAL management and labor unions insist that the company can avoid Chapter 11 by cutting costs and securing a $1.8 billion loan guarantee from the government, which is why the stock has nearly doubled since mid-October. But analysts have soured on the company's chances because the company is rapidly running out of cash and time, burning through nearly $8 million a day. And steep debt payments are coming due because the company can't meet the terms of its restructured loan agreements, forcing it to rely on grace periods while the government decides its fate. On Monday, the company was supposed to make a $375 million payment on enhanced equipment trust certificates, or EETCs, which are the bonds that back airplane leases. As expected, the company took out a 10-business-day grace period to avoid going into default and won't have to make a payment until Dec. 13. Meanwhile, UAL has run into problems with German bank Kreditanstalt fur Wiederaufbau, even though it had restructured its $500 million debt with the bank last month. The "debt held by a German bank had ostensibly been refinanced until 2007," Higgins said. "As it turns out, that debt became due yesterday." UAL failed to meet all of the conditions of its refinancing with KfW and now has a week to make that payment.