NEW YORK: Roger Federer (pic) was given a free ride into the US Open quarter-finals when his opponent Mardy Fish withdrew because of undisclosed health concerns, Reuters reported.

The decision was the latest setback for the 23rd-seeded Fish, who missed part of the season because of a heart ailment and had treatment for an unspecified illness after his gruelling third-round win over Gilles Simon late on Saturday.

"I regret that I have to withdraw from the US Open for precautionary measures," American Fish, who was set to clash with Federer on the Arthur Ashe Stadium centre court this morning, said in a statement.

"I was reluctant to do so, but am following medical advisement. I had a good summer and look forward to resuming my tournament schedule in the fall."

The decision means Federer, who has not dropped a set in this year's US Open at Flushing Meadows, advances to his 34th consecutive Grand Slam quarter-finals.

The 31-year-old Swiss will now play Tomas Berdych after the  Czech sixth seed thrashed Spain's Nicolas Almagro 7-6 6-4 6-1.

"I am really sorry for Mardy. I just want to wish him a speedy recovery. We all want to see him back on tour soon," said Federer, who owns an 11-4 career record against Berdych.

"It will be a tough match against Tomas. We have played many times in the past and he has always been a tough opponent. I will have to continue to serve well and dictate the points."

- mD