Roger Federer will be "very difficult to replace" once he calls time on his illustrious tennis career, according to his former coach Stefan Edberg.

The Swiss ace is widely considered as the greatest ever to step on the court, but is hugely revered for his endeavours off the court as well. Apart from entertaining millions of fans with his tennis, Federer also empowers a number of underprivileged children through his Roger Federer Foundation.

The 36-year-old's future in the game was called into question following his struggles with injury in 2016 and, having not won a Grand Slam since 2012, there were doubts if he would ever add to his tally of 17 major titles.

Federer, however, silenced his critics after winning eight titles in the last 12 months following his return from injury. He has also took his Grand Slam tally to 20 men's singles titles with his latest triumph at the 2018 Australian Open.

Edberg believes it will be impossible for another player to copy Federer in terms of the way he plays and the relationship he has with people – fans, reporters and sponsors.

"Roger is unique in many aspects," Edberg said, as quoted by Tennis World USA. "He still loves the game, is improving, has a big motivation, and is fit, which is something great considering his age. We all know that he plays tennis beautifully and that he is the best ambassador for this sport.

"He has a good relationship with the press and treats sponsors, fans in a unique way. He is perfect. It will be very difficult to replace him. He can't be copied."

Federer has displayed a new brand of aggressive tennis since his return from injury last season, which has contributed to his recent success. Edberg, who coached Federer for two years between 2013 and 2015, was in two minds when asked if the Swiss ace is a better player now than when he was in his prime.

"Maybe his four children keep him so young. But what's possible for him doesn't count for others. Is he a better player than what he was a decade ago? It's tough to say," the Swede said.

"You normally play your best tennis from 22 to 28. He may have dominated the Tour the most at that age, but look at last year. In some ways, he is a better player than 10 years ago, although he is not that fast."

Edberg, a six-time Grand Slam winner himself, also revealed the reason Federer employed his childhood idol as his coach.

"He wanted some changes in his game, which was the most important thing," the 52-year-old explained.

"He was coming from a difficult 2013. So he knew that something different was needed. He needed to become more aggressive and dictate on the court. In order to do so, you need a lot of motivation and need to do well physically."

Federer won 11 titles – but no Grand Slams – in two years with Edberg as his coach before the Swiss ace announced their split in December 2015.