KKR Financial also confirmed it is seeking to postpone payment of $5 billion in short-term securities.
News of the projections comes after KKR Financial this week announced that it had sold $5.1 billion of mortgage bonds, through which it has lost $40 million.
The estimated $290 million loss would arise from the firm disposing its remaining $5.8 billion of mortgage-backed securities and assuming liabilities of up to $50 million.
A statement from the firm said: "In light of the level of disruption and volatility in commercial paper and broader credit markets, estimates of potential exposure are necessarily subject to future revision."
Since the announcement of the losses, shares in KKR Financial Holdings have dipped 31 per cent.