"There is a great deal of uncertainty about whether the deal will proceed and, if it does, what implications it will have for the combined group's financial profile and financial policy in areas such as acquisitions, dividends, and debt," S&P said.
"If such a transaction were to occur, Standard & Poor's will treat it as a special event that is not currently factored in the ratings or outlook on Sual," the agency said on its Web site.
"Press reports about the transaction and related financial details (notably whether any pre-merger or merger-related cash payments are being considered) have not been confirmed by any of the companies involved," it said.
"Although we believe that a combined entity would enjoy a strong business profile, with a diversified asset base and a low cost profile, potential rating implications for Sual cannot be evaluated at this stage due to major uncertainty on the financial side," S&P said.