The Portuguese international, who left Old Trafford for the Bernabeu in 2009, has been linked with a return to the Red Devils.
However, the Daily Mail claims that United are willing to play hardball with Los Blancos after the player turned down the chance of a return 12 months ago in order to sign a new deal with the European champions.
United are said to be unwilling to throw money at a possible deal, knowing that a transfer fee and wages could add up to a combined £120m.
There is also believed to be little desire on United's part to match Ronaldo's tax-free earnings of around £300,000-a-week, with the risk of upsetting other high earners at the club.
Ronaldo scored a hat-trick in Real's 8-2 victory at Deportivo La Coruna on Saturday.