Jose Mourinho will demand £12million-a-year and Chelsea break the bank to sign Ronaldo if asked to return to Stamford Bridge.
Owner Roman Abramovich will also have to let the Portuguese have 'total control' of transfers and the training ground.
True cost: Chelsea will have to pay high price to lure back Jose Mourinho
Mourinho is high on Abramovich's wanted list to replace sacked Andre Villas-Boas.
Roberto di Matteo has been placed in temporary charge of the Blues until the end of the season.
Mourinho is expected to leave the La Liga leaders in the summer after falling out with Real president Florentino Perez.
Mourinho was spotted house-hunting in London last week and he has already stated his his intention to return to the Premier League.
Fed up: Real Madrid's Cristiano Ronaldo
Ronaldo is also said to have grown disillusioned with life at the Bernabeu after the fans turned on him despite scoring 96 goals in 88 games since his world record £80m move from Manchester United.
Abramovich has also reportedly sounded out Barcelona coach Pep Guardiola, who's contract expires in the summer.
But sources in Spain expect the 41-year-old to stay for at least one more season at the Nou Camp.
Germany coach Joachim Low has also been linked with the Chelsea hot seat, but claims in Switzerland that he met Abramovich at a Geneva hotel were denied. His present contract runs until 2014.