Winston-Salem - Two-time champion John Isner withdrew from the US Open tune-up event at Winston-Salem on Thursday with a left ankle injury.
American was due to play Lukas Rosol in the quarter-finals on Thursday,
but pulled out with the injury suffered in his win over Mikhail
Kukushkin on Wednesday.
"I am extremely disappointed to have to
withdraw from the Winston-Salem Open, one of my favorite stops of the
year," said Isner, who hails from North Carolina.
It wasn't yet
clear if the injury would affect 29-year-old Isner's appearance in the
US Open, which starts on Monday in New York.
Isner is seeded 13th
at the Open, and according to the draw released on Thursday could face
top seed Novak Djokovic in the fourth round.