DelPo ended #11 this year, skipped tournaments and didn't play consistently especially late in the year.
Pretty good ranking for not being near your best.
He should improve a lot, if just the endurance is improved without anything else he'll move up some spots.
Delpo was 65 points away from finishing in the top 10, despite his poor/mediocre slam results and skipping the final 2 Masters tourneys of the year. Not bad considering that he was ranked nearly 500 after the Australian Open.
Top 4 is a long way off being 11th, but with a year back on tour under his belt, there is no way that he fails to improve significantly on this season (especially considering his slam results this season).