Fed won Madrid and made the SF at Rome.
That means he has to defend 1000 + 360 points. He currently has 8715.
If he loses straight away in both (which is highly, highly unlikely) he will drop to about 7400 points.
Nadal has 6745 points. He is defending Monte Carlo, Barcelona and Rome. In Madrid he made it to 3rd round last year. That means he'll have to win every tournament he won last year and Madrid to gain points. If he does he'll gain 900 points. So he'll have roughly 7600 points.
So mathematically, unless I'm missing something, it is possible.
But in reality, it is very unlikely to happen. Federer has to have his worst clay season and Nadal has to have his best ever.
"Nadal is a good example of an counter puncher" - RF-18
"Cilic has huge serve too, so that gave Karlovic extra confidence" - jg153040