Greg Rusedski has warned Andy Murray still has a long road ahead if he is to return to the top of the game.
The former world number one has surprised many, including Rusedski, with the level at which he has been able to play only eight and a half months after hip resurfacing surgery.
In a three-week stint in China, Murray beat now world number 11 Matteo Berrettini and pushed Dominic Thiem and Fabio Fognini hard in close defeats.
It was a big step up from the performances Murray produced on his return to singles action in America in August and gave hope to his fans, as well as the Scot, that he could perhaps again challenge for tennis' biggest titles.
But, after two years of struggles with his right hip and at the age of 32, Rusedski believes it is too early to make future predictions.
The former British number one told the PA News Agency: "I've been pleasantly surprised. I thought it would be much more difficult for him, I thought it would take a little bit longer, but he's played very, very well.
The tournament at the O2 is shaping up to be a battle of the young challengers versus the old guard, with US Open finalist Daniil Medvedev the current front runner to be the best of the next generation.
Medvedev's success has reignited the debate about when a new face is going to win a grand slam.
"It's getting closer," said Rusedski. "I thought it was either going to be next year or the year after. Medvedev is the guy you're looking at who could possibly win one. It'll be a very exciting end of the season, which will set up 2020 beautifully."
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