NIE supplies 775,000 homes with electricity
The owner of Northern Ireland Electricity is expected to have a weak performance in 2009, according to a leading financial information firm.
Standard and Poor's (S&P) has also lowered Arcapita's credit rating for the third time in less than a year.
It said the Bahrain-based bank saw its financial profile deteriorate significantly in 2008.
Arcapita bought NIE's parent company Viridian in 2006 for more than £1.6bn.
Last year it abandoned an attempt to sell Viridian.
Standard & Poor's credit analyst Mohamed Damak said the decision to downgrade the credit rating reflected their opinion of "Arcapita's high leverage in the context of a very difficult economic and investment climate, which has challenged Arcapita's business model, reduced the value of its assets, and put pressure on its financial performance."
Arcapita said it was disappointed at S&P's decision to lower its credit rating, and said it believed that S&P's negative view on the private equity sector overall is "causing our rating with them to suffer unduly."
"In recent months, we have de-leveraged our balance sheet, improved our liquidity position, reduced our exposure to the inter-bank lending market to an insignificant level and implemented a range of measures to reduce expenses in the business," the statement continued.
NIE said that it was funded separately from its owner and had an industrial grade credit rating.
A spokesperson added that parent company Viridian was in full compliance with its debt obligations.