Manchester United reportedly have the first option on Real Madrid superstar Cristiano Ronaldo, should the Santiago Bernabeu club decide to sell their most valuable asset.

Ronaldo left Manchester United for Real Madrid in a world record £80 million transfer in the summer of 2009, and has scored 166 goals in 165 appearances during his time with Los Blancos.

However, the 28-year-old's future with Real Madrid has been the subject of constant speculation this season, and a return to Manchester United has been touted as a possibility for Ronaldo.

It has now been revealed by The Sun that Manchester United will have first refusal on Ronaldo if Real Madrid are prepared to sell the Portuguese, although it would take a new world record to capture his signature.

The Sun adds that a transfer fee placed on Ronaldo's head of £120 million is freely discussed in high circles at Real Madrid, and Manchester United may struggle to justify paying such a significant sum for a player with little sell-on value.

Sir Alex Ferguson has reportedly said that Ronaldo would love to return to Old Trafford, but financing a deal may be another matter entirely for Manchester United.

Ronaldo scored 118 goals in 292 matches during six seasons with Manchester United, after joining the Red Devils from Sporting CP in the summer of 2003.

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