Sam Bankman-Fried transferred at least $4 billion in FTX funds to Alameda Research earlier this year, sources told Reuters.
The money included customer funds as well as those backed by FTX's native token FTT and shares in Robinhood.
The transfer came after Alameda suffered steep losses on crypto deals in May and June, the report said.
CoinDesk first reported last week that Alameda Research held a large amount of illiquid FTT on its balance sheet, spurring speculation that the trading firm lacked sufficient liquidity.
In a series of tweets early Thursday, Bankman-Fried issued a broad mea culpa regarding FTX, and said Alameda is "winding down" its trading.