Top seed Roger Federer reached the quarter-finals of the US Open without hitting a ball when Andrei Pavel pulled out with an injury on Monday.
The 16th-seeded Romanian withdrew with a herniated disc, allowing Federer to reach the quarter-finals of the tournament for the first time.
World number one Federer is looking to become the first man since Sweden's Mats Wilander in 1988 to win three grand slam titles in the same year.
The Swiss will meet either sixth-seeded American Andre Agassi or Sargis Sargsian of Armenia in the quarter-finals on Wednesday after his walkover against Pavel.
"It happened in the second game of the fifth set against (Hyung-Taik) Lee," said the Romanian referring to his 6-4 6-2 1-6 1-6 6-4 third-round victory on Saturday.
"I felt something on my serve but wanted to win the match and didn't think about it. Afterwards I spoke to the physiotherapist.
"He told me to get something to drink and eat and come back, and when I did that it had got worse and worse.