Following its Tuesday announcement of a $US38.56 billion or $A42.89 billion takeover bid for Potash Corporation of Saskatchewan, international rating agency Standard & Poor's listed on Thursday BHP Billiton Ltd's long term issuer credit ratings in CreditWatch.

Standard & Poor's said that the move pointed to negative insinuations for BHP's financial standings as the agency stressed that "in resolving the CreditWatch, we will assess the implications of this purchase on BHP Billiton's financial risk profile."

The rating agency added that it is set to re-assess the giant resource company's projected capital expenditures for its current development projects, with attending review too on BHP's proposed capital outlay for PotashCorp, currently the world's biggest producer of fertiliser.

According to S&P credit analyst Craig Parker, the downgrading of BHP's credit ratings would not be a remote possibility once the acquisition deal for Potash has been finalised.

Mr Parker said that it is likely that BHP would be seeing its rating to slide by one level to A, that is "if the acquisition proceeds at the current offer price and if BHP Billiton's capital-spending program is not moderated.