Amazon.com

(AMZN) - Get Report

was down 6.1% in early trading, matching its 52-week low of $13.56, after

Lehman Brothers

urged investors to continue to avoid the online retailer's convertible bonds.

Ravi Suria, Lehman's vice president of convertibles strategy, said that without additional infusions, the company's working capital could fall below zero.

Suria said that as a result, Amazon could face a creditor squeeze in the second half.

He also said the company could have liquidity problems in the first half, and its recent results "have only increased our concerns."