Kokkinakis (shoulder) withdrew
from his second round match against Rafael Nadal at the US Open on Thursday.
Kokkinakis, who has dealt with one injury after another in his young career, was forced to pull out after he had picked up a four-set win in the opening round, which was just his third tour-level win of the year. The 23-year-old Australian, ranked No. 203, will now be forced to make another recovery as he attempts to work his way back to the main tour.