Roger Federer has admitted that we may never know who is the greatest tennis player of all time because the sport has changed so much.
The Swiss icon - who has won 20 Grand Slam titles, three more than Rafael Nadal's 17 in the all-time list of major winners in the modern era - believes players should be judged on their own generation rather than be compared to each other.
Federer - who lost 6-3 3-6 5-7 to Dominic Thiem in the Indian Wells Masters final on Sunday - could overtake Australian Ken Rosewall as the oldest winner of Grand Slam at the age of 37 if he can win one of the three remaining slams this season at the French Open, Wimbledon or the US Open.
"It's definitely difficult overall. I don't think Ken Rosewall was thinking of how many majors he was going to win. You know, I think the future is only going to be reminded even more so of what everybody has achieved," said Federer.
I think players 30 years from now are going to chase much more records than I did early on or Pete did or and so forth. And because the game was what it was, you know, it's very difficult to compare. To be quite honest, yeah, maybe you could do it in generations.
"But I think at the end of the day, it's just a fun and interesting debate, nothing more. We will never quite know because you only get sometimes the chance to be the youngest to win a slam, and you only get a chance later on to be the oldest to win something.