Ivan Lendl would be happy to coach Andy Murray for the rest of the Scot's career and believes he can get five times better.
The pair linked up at the start of this season and it has been an unqualified success, with Murray winning Olympic gold and then breaking his grand slam duck at the US Open.
The progress in Murray's game has been clear, with his forehand and second serve noticeably better, but it is on the mental side where Lendl seems to have had the most effect, instilling a belief in his man to maintain a positive approach.
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Lendl is in Prague this weekend for the Davis Cup final, hoping to see his home country win the title for the first time since he helped Czechoslovakia to the crown in 1980.
The 52-year-old said: "As long as it works for both of us, I can see myself being with him for the rest of his career.
"I have a lot of plans where I would like to see Andy end up with his game. I think [he can achieve] a lot more. I'm not going to say a number of grand slams, I'm just going to say where Andy is now. "I take point A – when we started working – now he's at point B, and when I envisage [where he can get to] I would say he's about 20% there."
After Murray answered the grand slam question, attention will now turn to whether the 25-year-old can end the long wait for a home winner at Wimbledon after his tearful loss to Federer in the final this year.
Lendl has no doubt that he can, and he said: "The question is 'is he going to win Wimbledon?' and know he will give it a good crack many, many times – not just once, not just in 2013 or 2014. He has quite a few years left in him and he's going to give it a crack."