The health insurer has been facing multiple headwinds this year and a turnaround may not happen quick for the stock.

UnitedHealth Group has attracted major contrarian investors like Buffett, Burry, and Simons. Click here to read why UNH stock is a Buy.

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.