Andy Murray must keep improving next season if he wants to stay at No. 1, according to Britain's Davis Cup captain Leon Smith.
Murray ended Novak Djokovic's 122-week reign at the top of the rankings earlier this month, and fended off the Serb from the year-end No. 1 spot by beating him in the World Tour final in London.
"You can imagine what his pre-season will be like," Smith told The Herald of his fellow Scot. "He will absolutely work his socks off and try to get better again.
"Now he is No.1 he has got to work out how to stay there and improve again. It never ends, never stops."
Murray will get his 2017 season underway 630 points ahead of Djokovic at the Qatar Open on Jan. 2, and could be set for a lengthy stay at No. 1.
In the first six months of the year, Djokovic must defend titles from Doha, the Australian Open, Indian Wells, Miami, Madrid and Roland Garros after a dominant start to 2016 -- indeed, he held a lead of more than 8,000 points over Murray after beating him in the French Open final on June 5.
However, it was just five months later to the day that Murray -- who first reached the No. 2 ranking in August 2009 -- ensured he would overtake the Serb by making the Paris Masters semifinals, in the midst of a career-best 24-match win streak that took in five consecutive titles.
That run capped off a remarkable season that also saw the Scot win a third major at Wimbledon, retain his Olympic gold in Rio and claim nine titles overall. His older brother Jamie Murray also had the best season of his career, winning two Grand Slams and finishing as the year-end doubles No. 1 with Brazilian partner Bruno Soares.
"What I find amazing is how much you have to put in to move from No. 2 to No. 1," added Smith. "You can go on an unbelievable run and go from No. 100 or whatever but to go from two to one, it was 21 matches in a row at that level of the sport, just to move one place.
"The bit that takes you from two to one is being prepared to ask, 'What do I need to do to make sure I get better?' I am hugely impressed about how he [Murray] keeps developing his game and Jamie is the same when you watch him operate on court and off the court. He has really committed to everything he has to do to make himself the best."