#2: Nothing left to prove at Real Madrid

Very few would disagree with the fact the Cristiano Ronaldo is the crowned jewel and the most important cog in the wheel who has helped usher a golden age at Real Madrid. His goal scoring exploits have seen Real Madrid become the first team to successfully defend a Champions League title.
To add to his chunk of records, the Real Madrid forward is already the all-time highest goal scorer for Real Madrid. He has won every vital award a legend has to have in his trophy cabinet.
A move to United might be even more appealing as he would have new targets to strike at Old Trafford. Ronaldo already has 118 goals for the Red Devils. Considering his ability to score at least 35 goals per season for over the next four seasons might see him become Manchester United's all-time top scorer. By toppling Wayne Rooney, he will be the first player in history to be an all-time top scorer for two different clubs.
That would prove to be quite a challenge for the 32-year-old Portuguese skipper.