While the "vote of confidence" from Buffett's investment validates the long-term value of UnitedHealth shares, the "management needs to regain trust and credibility with investors, and get back to its beat and raise reputation of the past," said James Harlow, senior vice president at Novare Capital Management.

As UnitedHealth Group wrangles with a federal investigation, an executive shuffle and a tanking stock price, a bullish ally has emerged: Warren Buffett. The Eden Prairie-based health giant’s stock price jumped more than 10% before trading opened Friday, following news that Buffet’s Berkshire Hathaway acquired about 5 million shares.