London - Novak Djokovic's domination of 2016 is not as inevitable as it might appear, former British No 1 Tim Henman believes, even if the other members of the "Big Four" will have to raise their game and hope the Serbian falters.
Djokovic won 11 titles including three of the four majors last year and has a 12-0 record this season, having thrashed Rafa Nadal, Roger Federer and Andy Murray to win the title in Doha and a record-equalling sixth Australian Open crown.
So impressive was the 28-year-old at Melbourne Park that many pundits believe a first calendar year grand slam in the men's game since Rod Laver in 1969 is on the cards.
Henman, while conceding there is now a gap between Djokovic and the other top players, does not think it has become a gulf.
"They can definitely challenge. Murray is at highest ranking in his career, he's No 2 in the world. He's playing great tennis," the 41-year-old Henman told Reuters in an interview.
"But obviously Djokovic is playing a little bit better at the moment.
"Roger was in the final of US Open last year and he was in the final of the Wimbledon last year. Djokovic stopped him in his quest to win more grand slams.
"They are still very, very close."
Henman thinks Federer, who won the last of his 17 major titles in 2012, and Murray look most likely to prevent a Djokovic grand slam sweep this year as Stan Wawrinka did at the French Open last year.
Nadal, who was knocked out of Australian Open in the first round, may not be the same player that won nine French Open titles but can still pose a serious threat on the clay courts at Roland Garros.
"The challenge for all those other players is to try and raise their levels and probably hope that Djokovic doesn't play quite as consistently," the former world No 4 and a four-time Wimbledon semifinalist said.
"There's no doubt right now that Djokovic is the player to beat."
Tennis is reeling from revelations in a report by the BBC and BuzzFeed in January that 16 players who have been ranked in the top 50 had been repeatedly flagged to the Tennis Integrity Unit (TIU) over concerns they had thrown matches.
Henman, who was in the city as the brand ambassador of HSBC Road to Wimbledon programme, a joint initiative by the All England Lawn Tennis Club and India's tennis body, said his first reaction to the allegations was one of "surprise" and called for more proof and not just speculation.
"If there has been any match-fixing then we need to make sure that it's erased from our sport because it's a crime in sports. We have no place for it in any sport let alone tennis," he said.
"It's also important to educate the young players so they appreciate this is something very, very serious if it has happened and make sure it never happens again."
"We have a tennis integrity unit and if they need to invest more money in that then we must do that. We must find out the facts and we then can move on from that."