|Australian Open 2017|
|Venue: Melbourne Park, Melbourne Dates: 16-29 Jan|
|Coverage: Live commentary every day on BBC Radio 5 live sports extra plus TV highlights on BBC Two from 21 January; live text on selected matches on the BBC Sport website. Play begins at 00:00 GMT|
Britain's Andy Murray says he needs to continue to improve if he is to remain world number one.
The 29-year-old Wimbledon champion replaced Novak Djokovic at the top of the rankings at the end of 2016.
Murray returns to Grand Slam action at the Australian Open in Melbourne next week, where he has been runner-up on five occasions.
"The reality is, in sport, that things obviously keep moving on, the game will get better," the Scot said.
"I'll obviously get older, the young guys will continue to improve, and also Novak, Roger Federer, Stan Wawrinka, Rafa Nadal and all the guys at the top are still going to be wanting to get there.
"I need to continue to improve. I for sure need to keep working hard.''
Murray's first-round match against unseeded Ukrainain Illya Marchenko is scheduled third on Monday on Rod Laver Arena, following Simona Halep v Shelby Rogers and Kateryna Kozlova v Venus Williams.
Play begins at 00:00 GMT.
Murray unfazed by new titles
Murray's successful 2016 - in which he also became Wimbledon champion for the second time and defended his Olympic title - ended with him being awarded a knighthood in the Queen's New Year Honours list.
But he says he has not been treated any differently by his fellow competitors.
"It kind of happened for me right at the end of the year, so I haven't been on the Tour much as the number one player," said Murray.
"So I haven't noticed it yet. I don't know if that will come over time, if I'm able to stay there or not."
Murray was also asked about Michael Downey's resignation as chief executive of the Lawn Tennis Association after only three years in the role.
He said it was "disappointing" and another example of short-term thinking at the top of British tennis.
"I think for a system that - maybe everyone would say - has not really worked for quite a long time, for change to happen you need someone, or a team, in there that's going to be in it for the long haul and not just a few years," he added.
'I'm clearly the underdog,' says Federer
Despite winning 17 Grand Slam titles, including four in Australia, Roger Federer said he was "clearly an underdog" in Melbourne.
"Yeah, why not for a change? I mean, I prefer to be the favourite. Underdog is OK," said Federer, who could meet Murray in the quarter-finals should they both progress.
The 35-year-old, who is returning from a six-month knee injury lay-off, is seeded 17th and will play veteran Austrian Jurgen Melzer, 35, who came through qualifying.
Federer v Melzer is the final match of day one on Rod Laver Arena.
Djokovic coy on Becker split
Second seed Djokovic starts the defence of his Australian Open title against former world number seven Fernando Verdasco of Spain, but will do so without the guidance of former coach Boris Becker, with whom he split late last year.
Djokovic, 29, would not be drawn on comments made by the German, in which he said the Serb had dropped his intensity in training which had contributed to a loss of form.
"We've had amazing success. It's all I can say. I don't want to go back and comment on anything," said Djokovic, who is looking for record seventh Australian Open crown.
"I kept a very friendly relationship with Boris. We just went separate ways."