The world number two suffered with pain in his knee just 24 hours before he took to the court against Kuznetsov.
"I had a fantastic week of practice with nothing of pain, not one bad feeling on the knee and not one place on my body. So I was really, really happy with everything," Nadal told a press conference. "But yesterday afternoon the most strange thing ever to happen to me. I was sitting on a chair in the hotel. I felt like a crack on the knee. It happens a lot of time with articulation, movement.
"After the second time, the knee stays with an unbelievable pain completely straight. I really couldn't move the knee like this. I have no movement on the knee.
"Seriously, yesterday during the evening I wasn't 100 per cent sure I would have the chance to play, because with the movement of that knee I felt that I will not be able to play."
Nadal's knee was heavily strapped as he defeated his American opponent in straight sets.