DENVER — Denver-based DaVita Inc. is selling its physician network arm for $4.9 billion. It will use the cash to buy back stock. The sale, to multifaceted health services company Optum, was to be announced early today. It will be completed next year after regulatory approval, according to a joint news release from the companies. The Denver Post reported that for $4.9 billion, Optum gets about 300 primary care and specialist clinics DaVita Medical Group operates, as well as 35 urgent-care centers and six outpatient surgery facilities. The group serves about 1.7 million patients each year. It will be combined with Optum’s OptumCare division, a network of about 30,000 affiliated doctors who serve millions of patients each year, according to the company. DaVita, a Fortune 500 company with a corporate headquarters housed in one of the newest office towers in downtown Denver, has a network of more than 2,400 kidney dialysis centers across the country. It also operates 230 dialysis centers in 11 countries outside the U.S. It first bought its physician network business, then known as HealthCare Partners in 2012. DaVita was valued at $11.2 billion as of Tuesday afternoon. Its stock was trading at $60.93 at market close, down 5.1 percent for the year.