For the seed for Roland-Garros, Ferrer is more than 3000 points ahead of Nadal.
Yes, it will be extremely hard for Nadal to get a top-4 seed in Roland-Garros (and he might have tougher draws than previous years in tournaments before Roland-Garros because of his lower seed)
Yeah, Nadal has to defend 3310 points, whilst Ferrer about 1075, because even if he doesn't go to any ATP 250, ATP 500 tournaments, his points don't drop out, except those that exceed 250 points. He has one 500 and one 300 = 250 + 50 = 300 points dropping. The other 775 points are from Mandatories. The difference between them now is 1465.
3310 - 1075 + 1465 = 3700 points must Nadal do without Ferrer defending any point. 4775 if Ferrer defends all points.
What does that mean actually? Nadal must score 3 Masters titles and win a bunch of 250s and 500s to secure his Best 6. Possibly also good results at the other 2 Masters. He doesn't play at one of them, so the mission gets even harder.
We should be getting used to the fact that Nadal is NOT gonna be 4th seed at RG.