Mardy Fish has admitted that it will be "tough" to beat world number two Andy Murray after winning his first ATP match in almost two years.
The American, who spent 18 months on the sidelines with a heart condition, beat world number 20 Viktor Troicki in straight sets at the Cincinnati Masters to set up a meeting with the British number one.
The 33-year-old, who is retiring after this year's US Open, told the ATP Tour website: "I was a little surprised at my level. I hadn't practiced a ton or particularly well for a little while. I was struggling with my serve.
"A friend of mine came in a couple days and helped, but it was still sort of a struggle even yesterday to sort of find my serve. I was obviously real happy with the level.
"[Murray is] pretty fantastic so far. He's won a ton of matches. He's won more matches than anyone this year, so he'll be tough."
Murray moved up to second in the ATP rankings after beating Novak Djokovic in the Montreal Masters final last week.
