Former Wimbledon champion Pat Cash claims Roger Federer has one more goal that he wants to achieve before he retires from tennis.

Federer won his 20th Grand Slam when he defeated Marin Cilic in five sets on Sunday (28 January) to win a second Australian Open title in as many years and further cement his status as arguably the greatest tennis player of all time.

It continues what has been a career renaissance that started last year in Melbourne as the number two ranked Swiss ace has now won three Grand Slams and an overall eight titles since returning to action in 2017.

Federer has long spoken of his desire to just enjoy the current wave of success that he has been experiencing over the course of the last 12 months.

However, Cash believes there is one thing he wants to do before his eventual retirement and that is to become the oldest world number one in tennis.

Thirty-six-year-old Federer's win on Sunday puts him just 155 points behind world number one Rafael Nadal and if results continue to go his way in the next few months, he could overtake the Spaniard and break Andre Agassi's record (33 years, 131 days).

"I think there's probably one last thing that he'd really like to do," Cash said on Eurosport via Express. "That is to be the oldest world No 1. I know that for a fact that he wants to be the oldest No 1.

"He had to defend his title to get that, of course he's got some other big titles coming up. Miami, Indian Wells, Wimbledon of course where he's always going to be the favourite.

"Rafa's just got to drop off, which he has, so he's going to edge closer to that. I think that will always be 'well, I've done everything now'."

Federer missed the opportunity to cap a remarkable 2017 as the world number one when he had to pull out of the Paris Masters in October last year.