The company board has appointed Stephen Hemsley, who has been the company's president and chief operating officer, to take over McGuire's chief executive officer title by Dec. 1.

The executive changes "will not have a critical bearing on the day-to-day operations," S&P credit analyst Shellie Stoddard says in a statement about UnitedHealth. "We believe [UnitedHealth] will continue its strong track record in operational performance under CEO Stephen Hemsley, new independent board direction, and significant bench strength in senior management."

But the findings of the review team "increase the potential for a significant restatement of prior-period earnings in connection with stock-option accounting, which could materially erode the quality of UnitedHealth's capital," S&P says. "The company and its accountants have yet to calculate the appropriate restatement if any for the stock-option plan, and an estimated range of outcomes is unknown."

UnitedHealth has postponed filing some financial reports because of the stock option problems.

Until all of the firm's SEC filings are up to date, UnitedHealth "leaves itself open to assertions of covenant default and possible unfavorable court interpretations, resulting in accelerated repayment of the debt security," S&P warns.

But UnitedHealth's subsidiaries appear to be doing well and should give the company a great deal of financial flexibility, S&P says.

Nevertheless, because of UnitedHealth's strong earnings capacity and generation of cash flows, S&P believes that the accounting and tax effects of the stock options problems are unlikely to be large enough to impair the company's operating performance or do much damage to its balance sheet, S&P says.

Operations should generate about $5.8 billion in cash flow this year, S&P notes.

S&P expects to see "limited loss of new or renewal business, minimal disruption in provider networks, and manageable financial cost and accounting restatement," the firm says.

Fitch points out that a group of persons that says it holds UnitedHealth debt securities has alleged that UnitedHealth already is in default of the indenture governing the debt securities.

"The company has stated that it believes it is not in default," Fitch says in a comment on the UnitedHealth option program announcement.

Fitch is waiting to see how regulators and shareholders' lawyers will respond to the review team report, the firm says.

But UnitedHealth still has a strong management team, good balance sheet fundamentals, a good balance of risk-based and fee-based businesses and a very strong earnings track record, Fitch says.

Fitch does not believe the developments announced so far significantly diminish UnitedHealth's ability to meet its debt and policyholder obligations, Fitch says.

In related news, news organizations have reported that McGuire's contract requires UnitedHealth to pay him $5.1 million per year. UnitedHealth reported Sunday that it is still talking to McGuire about the terms of his departure.