Simon Property Group is preparing a revised bid for its biggest rival, bankrupt General Growth Properties to be presented within a week, according to a source with knowledge of Simon’s plans.

Simon’s lawyers sent a letter to General Growth’s attorneys last night, according to the person, who asked not to be identified because the correspondence is private.

The story was first reported by the Wall Street Journal.

Simon, the largest US mall owner, last month offered more than $10 billion for General Growth, which called the bid too low. The Chicago-based company said it instead plans to split itself in two to exit bankruptcy with financing from a group led by Brookfield Asset Management Inc.

General Growth filed the largest real-estate bankruptcy in U.S. history in April after amassing $27 billion in debt making acquisitions.