Texas Pacific Group, Bain Capital and Goldman Sachs Capital agreed to buy the chain in July.
However, according to the Times today, the bankers to the Texas Pacific consortium, JP Morgan Chase and Schroder Salomon Smith Barney, are struggling to raise the finance to fund the deal.
It is understood the debt must be in place by the end of the year or the deal will collapse. The consortium planned to fund about $1.6 billion of the $2.26bn price using debt, with about $500m of that to be raised from the sale of high-yield bonds.
However, investors' appetite for debt has weakened, and there is speculation that Burger King's sales have fallen since the agreement was signed in July, according to the Times.