Jefferson Smurfit, the Irish paper and packaging company, is likely to lose its investment-grade credit rating once it reveals plans to refinance its €3.7bn ($3.6bn) takeover by Madison Dearborn Partners, the US private equity firm.

Standard & Poor's, the international ratings agency, maintained Smurfit's BBB+ rating on CreditWatch with negative implications last week after more than the required 80% of the company's shareholders approved the takeover.