Mardy Fish had to withdraw from his fourth-round matchup with Roger Federer at the U.S. Open on Monday, just hours before the match was scheduled to begin. Not much reason was given at the time other than citing "health issues" in the withdrawal.

U.S. Open Day 8
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"I regret that I have to withdraw from the U.S. Open for precautionary measures," Fish said. "I was reluctant to do so but am following medical advisement. I had a good summer and I look forward to resuming my tournament schedule in the fall."

Fish, who did miss time earlier this year with heart concerns, spoke with Justin Gimelstob of CBS Sports, a close friend, and shed a little more light. Gimelstob explains in the video above that the pressure of the tournament and physical toll thus far was too much for he and his heart to handle. So to be safe, he was advised to withdraw, which he did.

It's an awful turn of events for Fish as the U.S. Open is as big as it gets for him in the spot, being his home nation's Slam and all. But some things are just more important, even if they're precautionary.

The ironic part, as Gimelstob points out, is that there was very little pressure on Fish going into his match with Federer. There were really no expectations for him to beat the world No. 1 so he was playing with the metaphorical house money. What that doesn't factor in, though, is the pressure that Fish puts on himself, the stress that can cause. No athlete goes into a match conceding he/she will lose. Believing you can win is a necessary psychological element to competition at the highest level.

Federer, while undoubtedly happy to be onto his 34th consecutive Slam quarterfinal, wasn't necessarily happy with how it happened. Being the true competitor that he is, it wasn't how Federer wanted to advance and of course he didn't want to see it happen to his opponent, Fish. He shared his well-wishes in a statement.

"I am really sorry for Mardy," the statement said. "I just want to wish him a speedy recovery. We all want to see him back on tour soon."