Not seemingly during this half of the year. I read that since Fed lost in Dubai - and was the def. champ - Nadal can close to within 125 points if he takes the title (but has to beat Roddick and Djokovic on the hardcourts there). So what's coming up? Indian Wells and Miami, where Federer has very few points to defend (R64, R16 respectively). Nadal? Way more points to defend (W, QF), which means anything short of those results equals a drop in total ranking points. And even into the claycourt season, Nadal has nowhere to go but down (4 W, 1 RU in '07).
Do any of you think there will be some exchanging of the #1 ranking this year? Like back to the early 90s with Becker, Edberg, Courier, etc.