Murray is ready despite frying against Fish

Andy Murray insists he is ready for the US Open despite struggling in the heat as he lost to Mardy Fish in the quarter-final of the Cincinnati Masters.

The Scot was visibly suffering in the second set as temperatures reached 34 degrees, and also received treatment on an apparent knee problem, as Fish came through an energy-sapping contest 6-7 6-1 7-6 in two hours, 56 minutes.

The world No 4 looked out on his feet at times between points in the third set but did not hold back during them before finally bowing out of the tournament.

"I have put in a lot of work off the court," said Murray, who won the ATP Rogers Cup in Toronto before heading to Cincinnati. "I've worked as hard as I can to get in good shape. I just tried to fight as much as I could, and nearly won. I've had more than enough matches before the US Open."

The final Grand Slam of the year gets under way in New York on 30 August. Murray saved two set points in the tie-break before clinching the first set but looked a different player in the second as injury and the heat of the day appeared to take their toll.

The American raced into a 4-0 lead, Murray feeling his knee in the second game and then complaining of dizziness at the change of ends after the third game. The 23-year-old got on the board in the set to make it 4-1, an ice pack being applied to his leg after the game but Fish rattled through the next two games to level the match.

Murray, though, was in no mood to throw in the towel in the deciding set, saving two break points to prevent Fish taking a 2-0 lead. He then forced a host of deuces on the Fish serve before the American managed to move 3-2 in front, with no breaks taking the decider into another tie-break.

Murray moved 4-2 ahead but a successful challenge gave Fish the advantage at 5-4 and the 28-year-old from Minnesota closed out the match.

Meanwhile, the world No 1 Serena Williams will miss this year's US Open after failing to recover from a foot injury. Williams, 28, has already missed three tournaments since cutting her right foot on broken glass in Munich in July. "It is with much frustration and deep sadness that I am having to pull out of the US Open. My doctors have advised against my playing," the Wimbledon champion said.

Williams said missing the tournament at Flushing Meadows was "one of the most devastating moments of my career".

She suffered the injury shortly after winning her fourth Wimbledon singles title last month. It was before playing in an exhibition match against Kim Clijsters in Belgium on 8 July, an event which drew a world-record crowd for a tennis match of 35,681.

Williams underwent surgery in Los Angeles on 15 July but will now miss a Grand Slam for the first time since Wimbledon in 2006.

She has played only six tournaments this year, including the other three Grand Slams. Victories in Australia and at Wimbledon took her career record to 13 Grand Slam titles. Last year, she lost in the semi-finals of the US Open after a furious outburst at a line judge over a foot-fault call in her defeat by eventual champion Clijsters.