This would be close. I think Nadal's retreiving and spin (which wouldn't be so thoroughly hindered as to be ineffective) would overpower Muster's fitness.
Nadal is probably the best, or second best, dirtballer ever.
Allcourter. Tennis fan. Head Youtek IG Speed MP 315 18x20: Klip Legend 16/Big Hitter Silver 16 55 lbs.