London: Scotsman Andy Murray's achievement in becoming men's tennis world number one is exceptional, women's tennis legend Martina Navratilova told the BBC on Sunday.
Murray, 29, moved to the top of the rankings for the first time in his career after replacing long-time incumbent Novak Djokovic, when Milos Raonic pulled out of their semi-final in Paris on Saturday.
The Scot's climb to the ATP rankings' summit -- the first Briton to do so since computerised rankings came in in 1973 -- caps a remarkable year which has seen him win a second Wimbledon crown and mount a successful defence of his Olympic title in Rio.
"Since Roger Federer became number one its been him, Rafael Nadal and Novak Djokovic at the top of the rankings," Navratilova told BBC Radio.
"Its some pretty rarefied air to get into as its been a pretty exclusive club for some time.
"To get to number one is an exceptional thing, it's an amazing accomplishment.
"The fact it came this late in his playing career shows how determined and focused he is," she added.
Navratilova, who spent 332 weeks atop the women's standings and accrued 18 Grand Slam singles titles, said Murray had shown real character to battle his way to the top ranking.
"To keep going and going and thinking I can improve is testament to his character," the 60-year-old said.
Murray's predecessor as British number one Tim Henman -- who was ranked a career high fourth in the world on three occasions from 2002 to 2004 -- believes he can stay at the top for a while to come.
"I don't think Andy was ever going to settle for second best," Henman told BBC Radio.
"Now he's reached number one I don't think for any moment in time he's going to take his foot off the gas.
"If Andy stays fit and healthy, I can see him being the dominant force going forward.
"If you're going to put a number on it, you'd like him to get to 52 weeks at the top. Who knows from there?" added the 42-year-old, who reached five Grand Slam singles semi-finals.