While holding a two-sets-to-one lead over Marin Cilic, Nadal required treatment on what appeared to be a hip problem and it eventually led to the Spaniard pulling out of the contest after falling 2-0 down in the final set.
Nadal will now have an MRI scan on the injury, but the 16-time Grand Slam winner has stated - not for the first time - that the players are not benefitting from the frequent change in court surfaces during a calendar year.
The 31-year-old is quoted by BBC Sport as saying: "Somebody who is running the tour should think little bit about what's going on. Too many people are getting injured.
"I don't know if they have to think a little bit about the health of the players. Not for now that we are playing, but there is life after tennis.
"I don't know if we keep playing in this very, very hard surfaces what's going to happen in the future with our lives."