Both Nadal and Murray have shots to gain the no 1 rank at the USO. Next week Nadal will be at 8665 points. Federer will be at 11040. Murray will be between 8610 and 9250. This will be going into Cincy. Rafa will be 2375 points behind Fed. Murray will be between 2430 and 1790 points behind.
So thinking here, but the best chance for both guys would be to draw him in the semis beat Fed there, then win the title. Of course, Murray will likely be no 2 so for him to get the no 1 rank hed have to hop that someone else beats Fed before or at the semis.
It will be hard to do, especially since Nadal is far from good form, and Murray has been far from great in the slams this year