Roger Federer
Roger Federer is a major contender for being the GOAT in tennis. In this picture, Federer takes part in a press conference after losing to South Africa's Kevin Anderson 2-6, 6-7, 7-5, 6-4, 13-11 in their men's singles quarter-finals match on the ninth day of the 2018 Wimbledon Championships at The All England Lawn Tennis Club in Wimbledon, southwest London, July 11, 2018. FLORIAN EISELE/AFP/Getty Images

Roger Federer is considered by many as the greatest player of all time (GOAT) in tennis, but the Swiss legend believes the unofficial accolade is very much open to debate.

Federer won his 20th Grand Slam earlier this year and has won 10 singles titles since the start of 2017 to further his claim as the GOAT of the sport, especially as he turned 37 earlier this month. In addition, he is the oldest No. 1 in tennis history and holds the record for most number of weeks as the top-ranked player in the sport with 310. He also holds a record eight Wimbledon wins.

However, an argument can be made for others as well. World No. 1 Rafael Nadal has a 23-15 winning record over Federer and most recently won his 17th Grand Slam title at the French Open. The win at Roland Garros made it 11 French Open wins for the Spaniard with no other player winning a single event, let alone Grand Slam, 10 times.

He is also the youngest player to have achieved a Career Grand Slam when he accomplished the feat at 24, while he has the most Masters 1000 wins with 32.

Meanwhile, Novak Djokovic won his 13th Grand Slam at Wimbledon last month and at his peak, was a serious contender for the GOAT accolade. The Serbian ace is just the third player in history to hold all four Grand Slams at the same time while he has also won an Open era record six Australian Open titles.

Most impressively, he has a rare winning record over both Federer and Nadal, being the only player to defeat them in multiple Grand Slam finals as well as in all four majors. Djokovic also holds the distinction of beating Federer in two Wimbledon finals while he is just the second player to defeat Nadal at the French Open.

Arguments could be made for the past greats as well and that is why Federer believes nobody will quite know who was the unanimous GOAT of the sport, especially with how it continues to evolve.

"For me, there is clearly a discussion, because we’ll never quite know anyways," Federer said, according to Tennis 365. "I think with amateur tennis we had before, going into professional tennis, the Grand Slams are getting somewhat more important over time. More players travelling to all the slams, not skipping Australia anymore."

"It’s all changed in the last 25 years, I’d say. Before they also had different rankings, which was an average ranking over the tournaments you played, so you wouldn’t play on your weak surface. Now it doesn’t matter anymore, just the best 18 tournaments count, so it’s changed in tennis over the years," he said. "It makes you play differently in different types of tournaments throughout. Obviously, today, probably we chase more the records than they used to in the past. Keeps us on tour longer. I think we’re doing more to stay more injury‑free. There are so many guys that did so many great things."

"Some were unbelievably young when they achieved some great things, some were on the older side when they achieved great things. Yeah, then there’s streaks and stuff. Whatever you look at, I think it’s a very open debate," he added.