The Portuguese winger, who scored the winner to knock United out of the Champions League last week, has long been linked with a return to Old Trafford.
According to The People, United's future sponsors General Motors are keen for the club to make a marquee signing and will help with the costs.
United have already agreed a shirt sponsorship deal with GM through Chevrolet, and the American car giants are even willing to buy out the last year of Aon's current deal.
That would allow them to assist with the reported £55m fee for Ronaldo as well as his £10-a-year wages.
It is rumoured that Madrid will look at Gareth Bale to replace Ronaldo, although the Welshman is keen to stay at Tottenham Hotspur until at least next summer.