He is seeking the remainder from other funds, including current investors in FTX such as venture capital fund Sequoia Capital, the source added.
Bankman-Fried told investors that Alameda owes FTX about $10 billion, the Wall Street Journal reported.
FTX had lent more than half of its customer funds to Alameda, the newspaper said.
The U.S. securities regulator is investigating FTX.com's handling of customer funds and crypto-lending activities, according to a source with knowledge of the inquiry.
Canada's Ontario Teachers Pension Plan, Tiger Global and Japan's Softbank are also FTX investors.