3. His Age
As already stated, there is very little chance of Ronaldo leaving Real Madrid before his contract expires in 2015, due primarily to the insane amount of money any potential suitors would have to fork out on the star. Providing the Portuguese ace doesn't sign a contract extension at the Bernabeu, which cannot be ruled out as a possibility, he will be leaving Real at the age of 30. By then, will the player we see today be of the same ilk? His mantle of "world's greatest player" will likely have been passed on to a more youthful protégé such as Neymar and his irresistible powers may have started to wane by the time his Real career draws to a close. It's unlikely that he'd be allowed to leave for nothing in 2015 considering the inordinate sums of money Real invested in him to begin with, and if a new deal at the club doesn't materialise, Madrid would likely be swayed into selling up next summer. He will still be a world-class player by then, but at 29, will he be worth the £30 million + needed to buy him? United have a policy of not signing a player with limited to no re-sale value, and though they made an exception to that rule with Robin van Persie, it remains to be seen if they do so again.