In June, Reynolds swooped in to buy Graham Packaging, beating out rival Silgan Holdings with a US$1.68 billion cash offer.
The packaging empire had previously flagged it would take on as much as US$5 billion of new debt to fund the takeover.
Reynolds expects to realise US$75 million in cost savings, and says it anticipates a net leverage ratio of 6 times adjusted earnings before interest tax, depreciation and amortisation.
Still, the rating agencies aren't entirely down on Hart, with Moody's saying Reynolds Group has strong brands and market positioning and is "anticipated to continue to generate some level of free cash flow" which will go into paying down debt.
S&P says Reynolds has a strong business risk profile and is the world's most diversified consumer and foodservice packaging company, even with its "highly leveraged financial risk profile."
The Graham purchase will bring Hart close to being the biggest packaging company in the world, with Tetra Laval Group's annual revenue at 9.99 billion euros (US$14.25 billion) and Hart's sales set to rise to US$13.26 billion, based on pro-forma figures released by Reynolds Group.