He is scheduled to play 5 out of the next 6 weeks straight before the USO (Atlanta, Washington, Cincinnati, Montreal, and Winston-Salem). Why on Earth would he do this? I know it's his best surface but why Winston-Salem? At least get some rest before the Slam.
He needs matches. He can't assume after all the time off he will be in top form. My guess is if he makes a couple decent runs in the Masters he will pull out of the NC tournament.