As a outcome, Marca believe that "unless there is a drastic change in the coming days, there will come a point of no return for Ronaldo".
United's executive vice chairman Ed Woodward has long-dreamed of luring the five-time Ballon d'Or victor back to Old Trafford.
Real Madrid themselves appear to be playing hardball, and President Florentino Perez maintains that Ronaldo is under contract for another three years and will therefore will remain in the Spanish capital for the foreseeable future.
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Real are believed to be open to the idea of selling the 33-year-old, following Zinedine Zidane's resignation as manager last month.
Besides Zinedine Zidane's sudden departure, Real's speculated interest for Neymar has also complicated matters for Ronaldo as the club is reportedly preparing to offer a world-record bid to bring the Brazilian from Paris-Saint Germain forward.
Ronaldo has a contract with Real Madrid until 2021.
Real Madrid star Cristiano Ronaldo wishes to stay in Europe if he carries out his threat of leaving the Spanish capital this summer - ruling out any potential move to Major League Soccer or the Chinese Super League at this stage of his career.