Former Indian tennis star Vijay Amritraj claims Roger Federer's record of 20 Grand Slam titles can be broken, despite his current achievement looking "insurmountable" at this point of time.

After winning the Wimbledon in 2012, the Swiss tennis ace struggled to win even a single Grand Slam title until the end of 2016. He was forced to stay on the sidelines due to a knee injury, which even forced him to miss the 2016 Rio Olympics.

However, Federer bounced back and started 2017 by winning the Australian Open. He also won the Wimbledon last year to make his eighth title, which is the record for most number of titles at SW19.

The 36-year-old started 2018 by adding one more Australian Open title to become the first tennis player to win 20 Grand Slam titles. Amritraj gave examples of former tennis stars' records, which were broken and believes Federer's current record for most number of Grand Slam titles could still be surpassed by another tennis player in the future.

"You know, we should never say never, as you all know. We thought ever since Roger Bannister [middle-distance athlete] broke the four-minute mile, that it wouldn't be broken. But it was broken. We though [Bjorn] Borg's five Wimbledon wouldn't be broken," Amritraj told NDTV.

"It was broken by Pete [Sampras] and then we went to Roger. So it happened as we go along. This 20 majors Roger has won seems completely insurmountable."

10-time French Open winner Rafael Nadal is second in the table with 16 Grand Slams. The Spaniard is set to be the favorite to win the 2018 Roland Garros, provided if he remains fully fit for the second major event of the calendar year in Paris.

Roger Federer
Roger Federer became the first tennis star to win 20 Grand Slam titlesGetty Images

Federer also climbed to the top of the ATP rankings in February at the 2018 Rotterdam Open. Amritraj explained how a technical change has helped the oldest world No.1 to regain his best form even at this stage of his career.

"The one thing you cannot do is bet against greatness. This is as great as they come. In my opinion, his work ethic has matched his desire. That's hard to do at this stage of your career, the twilight of your career," the two-time US Open quarter-finalist explained.

"What he is able to achieve by winning the Australian Open, to be able to come, last year he won the Indian Wells and the Miami Open and this year he reached the final. He is playing some of the finest tennis we have seen him play ever since he switched the guts, the racket.

"Started to move forward, [Ivan]Ljubicic has helped with his back-hand. All of these have made a huge technical difference to the way he is played the game, since now, since 15 years ago."