American Mardy Fish has pulled out of his fourth-round match against Roger Federer at the U.S. Open because of "health reasons."

Tournament officials did not immediately provide further details Monday on Fish's ailment. The 30-year-old missed about two months this season because of an accelerated heartbeat and had a medical procedure in May.

His third-round match against Gilles Simon went five sets, lasting more than 3 hours and ending after 1 a.m. Sunday.

Afterward, the 23rd-seeded Fish did not appear at a news conference. Tournament officials said he was getting treatment, but didn't give any specifics.

The top-ranked Federer reaches his 34th consecutive Grand Slam quarterfinal.