Ronaldo has just two years left on his contract at Madrid and is known to be disillusioned with life at the Santiago Bernabeu, at the end of his fourth season there.
The Ligue 1 club, funded by Russian billionaire Dmitry Rybolovlev, have already spent over £110m this summer on Radamel Falcao ofAtletico Madrid and James Rodriguez and Joao Moutinho of Porto. The Independent in London reports this morning that they are now prepared to make their boldest move yet, taking advantage of the Portuguese forward's frustration at Madrid, and failure to sign a new deal, to tempt him to join with a world record salary offer of €20m (£17m) per year.
Monaco are closely monitoring Ronaldo's negotiations with Real Madrid over a contract extension, and if no deal is done by late July or August they will make their move. There have been talks between Monaco and Ronaldo's camp over the last 18 months and the two parties met earlier this year.
Ronaldo feels underappreciated at Madrid and believes he is due a pay rise. He is especially keen to earn more than his great rival Lionel Messi at Barcelona. In February of this year, Messi signed a new contract with Barcelona that will last until 2018, heavily incentivised but with a basic salary starting at €12m per year, but increased through bonuses and image rights.
Monaco will offer Ronaldo an annual salary of €20m, which would equate to nearly £330,000 per week. The principality of Monaco does not charge its residents income tax and so Ronaldo would become the highest-paid footballer in the world.
Zlatan Ibrahimovic, who would be his Ligue 1 rival at Paris Saint-Germain, has a net salary of between €13m and €14m but because of France's near 75 per cent tax rate on top earners, Paris have to pay out far more than that. Monaco would face no such issue.
This summer, since their promotion back to Ligue 1, Monaco have spent more than £100m on players, all of whom are clients of Ronaldo's agent, Jorge Mendes. Their summer spending started with a combined £60m on the Porto pair Rodriguez and Moutinho – both of whom are Mendes players, as is Ricardo Carvalho, formerly of Chelsea and Real Madrid, who arrived on a free transfer.
Their next purchase was Falcao, the Colombian forward who joined from Atletico Madrid for a fee of roughly £50m, and will be paid £12m annually.Victor Valdes, the Barcelona goalkeeper, is likely to be the next arrival. They have also been linked with John Terry.
Monaco would have to bid another world record fee for Ronaldo, as Real Madrid would be keen to make back the €95m (£80m) which they paid Manchester United for him in 2009. United are also keen on Ronaldo's signature this summer, with the player himself open to the possibility of returning to Old Trafford, where he enjoyed six brilliant seasons between 2003 and 2009. There has also been ongoing dialogue between Ronaldo's camp and United over the past six months.
Ronaldo has scored an implausible 199 goals in 201 games at Real Madrid since his arrival from Manchester United in 2009. Only the feats of Messi at Barcelona have stopped Ronaldo from being recognised as the undisputed player of his generation.
But, with one Spanish title and one Copa Del Rey in four years of individual brilliance at Madrid, he has not done as well as he could have. In those four years, Messi has won three Spanish titles, the Champions League, a Copa Del Rey, the Club World Cup and, importantly, three Fifa Ballon D'Or awards. Ronaldo has not been crowned the world's best since his 2008 Ballon D'Or and would love to win it again. Last September, Ronaldo declined to celebrate two goals that he scored for Madrid, explaining that it was because he was "unhappy" with the club.
Top billing: World record transfers
Cristiano Ronaldo (Man United-Real Madrid) £80m
Zlatan Ibrahimovic (Internazionale-Barcelona) £56m
Kaka (Milan-Real Madrid) £55m
Hulk (Porto-Zenit St P'burg) £52m
Radamel Falcao (Atletico Madrid-Monaco) £50m
Fernando Torres (Liverpool-Chelsea) £50m
Neymar (Santos-Barcelona) £48.6m
Zinedine Zidane (Juventus-Real Madrid) £48m
Falcao (Porto-Atletico Madrid) £41m James Rodriguez (Porto-Monaco) £38.5m
Sergio Aguero (Atletico Madrid-Manchester City) £38m
Luis Figo (Barcelona-R Madrid)£38m
Hernan Crespo (Parma-Lazio) £35.5m