In the latest sign of growing investor scepticism over their business model, Australian financial firms Macquarie Group and Babcock & Brown took steps Monday that could indicate a further retrenchment of their funds from public markets.

Under their complex model, known as the Macquarie model or the managed infrastructure model, the two companies manage funds that own cash-generating assets ranging from toll roads to airports to wind farms. The funds are debt-reliant and often publicly traded.