World number one Roger Federer received a walkover into the US Open quarter-finals Monday when America's Mardy Fish withdrew from their last-16 tie due to "health reasons", an event spokesman said.
Five-time champion Federer will face either Czech sixth seed Tomad Berdych or Spanish 11th seed Nicolas Almagro for a place in the semi-finals.
It will be the top seed's 38th Grand Slam quarter-final.
"Mardy Fish has withdrawn for health reasons," said the spokesman.
Fish, 30, missed two months of the season earlier this year because of a heart problem.
He was hospitalised after the Miami Masters in March when his heart rate increased to three times its normal resting rate.
The American then underwent a procedure called a cardiac catheter ablation in Los Angeles on May 23 to correct faulty wiring in his heart.