Andy Murray has admitted he must improve if he is to win a Grand Slam.
Murray, 24, lost to Rafael Nadal in four sets at the US Open, the third successive time the Scot has lost to the Spaniard in a Grand Slam semi.
"I've got to improve," Murray said. "I need to work on my game and get physically stronger.
"If you play the right way against Nadal you can make him do the running and dictate play. But I didn't do that in the first two sets," he added.
Murray, who went down 6-4 6-2 3-6 6-3, has won only two sets in his three Grand Slam semi-final defeats by Nadal this year.
"It's always tough playing Nadal who, in my opinion, is the greatest player to play tennis," said the Scot.
"I was disappointed with the first two sets but the third and fourth were better. I know the right tactics for playing against Rafa but I didn't implement them in the first two sets.
"It's very easy from the side to suggest what I should be doing out there - you should see some of his passing shots. There's many things I could have done a bit better but I didn't."
But Murray maintains belief that he can win a Grand Slam.
"If you want to judge someone's whole career based purely on slams then I would have had a terrible career but I don't really feel like I have," he said.
"There have been things I've done well and I've still got three or four years where I'm playing tennis at my peak."
Australian tennis legend Rod Laver believes Murray has the talent to win a Grand Slam but must make some fundamental changes to his game.
"Andy tends to play a wait-and-see game rather than taking the game to the opponent," Laver told the BBC's Sportsweek programme.
"He doesn't need a new coach for stroke production but maybe for how to play a certain opponent. That may help getting Andy a Grand Slam.
"But Murray hasn't improved enough to beat Nadal. He plays good tennis and certainly volleys well but a few points got away from him. He doesn't play the important points as well as he can and needs to tighten up and make the other player work harder to win that point.
"He's certainly capable of winning a Grand Slam."
Laver, who won 11 Grand Slams, added that Nadal was "a great champion".
"Nadal has proved that he is so consistent and a great fighter and it's tough to break through that. Murray played well, including a good third set, but Nadal is just too tough," said the Australian.