Roger Federer "always believed" he could win another grand slam and return to the summit of men's tennis, despite being struck down with injury 18 months ago.

Since spending six months out of the sport due to a knee problem, the Swiss legend has taken his major tally to 20 with successive wins at the Australian Open and an eighth title at Wimbledon.

As Federer sat on the sidelines, Novak Djokovic and Andy Murray dominated 2016, with the latter finishing the year as world number one. At the same time, Rafael Nadal returned to form and full fitness and won a 10th French Open and the US Open.

But the 36-year-old said, according to AD: "I would have been in the clouds with winning one grand slam. In 2016, Novak, And Andy were at their best and Rafa was young enough for a comeback. I always believed that I could do it again."

The more immediate concern for Federer is the prospect of returning to world number one, which he can do this week at the Rotterdam Open.

Should the veteran reach the last four at the ABN Amro World Tennis Tournament he will replace Nadal at the top of the ATP standings and return to the summit for the first time since October 2012.

An assault on Nadal was only made possible by Federer retaining his Australian Open crown in Melbourne with victory over Marin Cilic in five sets.

Tony Godsick, Federer's long-time agent, immediately contacted tournament organisers in the Netherlands to discuss the possibility of accepting a wild card after the win Down Under with the announcement regarding his participation only made last week.

"Our team is very excited, so I'm here, I'm giving myself a chance," he explained, according to NU Sport. "I have to be here with all my heart and run behind.

"Then I already thought about the world ranking," he says. "I did not expect to win in Melbourne, it was so long ago that I had extended a grand slam title, and then I knew that Rotterdam was an option."

Federer begins his campaign in Rotterdam against Ruben Bemelmans on Wednesday (14 February) and is on course to face Stan Wawrinka in the quarter-finals, where victory would be enough to take him back to the top.

"If I can recapture the highest position, I do not want to do it in a simple way. I would love to be in this [quarter-final] position against anyone. It would really be an incredible achievement, it's nice that Stan is in the same half of the schedule as I am."

Roger Federer
Federer can go back to world number one this week in Rotterdam. Getty Images