Nadal leads on 9,760 points with Federer a close second on 9,605. However, the Swiss is playing this week at the Rotterdam tournament and with Nadal not in action, a run to the semi-finals would return him to the top of the pile.
The 20-time grand slam winner Federer would become the oldest man to top the rankings should he take the number one placing.
Lower down the top 10, German Alexander Zverev moved up a place to fourth ahead of Bulgaria's Grigor Dimitrov.
ATP top 10 as of February 12 (previous ranking in parenthesis):
1. (1) Rafael Nadal, Spain, 9,760 points
2. (2) Roger Federer, Switzerland, 9,605
3. (3) Marin Cilic, Croatia, 4,960
4. (5) Alexander Zverev, Germany, 4,450
5. (4) Grigor Dimitrov, Bulgaria, 4,425
6. (6) Dominic Thiem, Austria, 4,060
7. (7) David Goffin, Belgium, 3,400
8. (8) Jack Sock, United States, 2,880
9. (9) Juan Martin del Potro, Argentina, 2,815
10. (10) Pablo Carreno-Busta, Spain, 2,705