Andrea Petkovic has revealed that she thinks Roger Federer would have stopped at 17 Grand Slam titles if not for the challenges posed by Novak Djokovic and Rafael Nadal.

Former world No. 1 Federer is known as one of the greatest tennis players of all time. Across his long career that lasted over two decades, the Swiss player won 20 Grand Slam titles, including a record eight victories at Wimbledon. Throughout most of his professional career, Federer's main rivals were fellow Big Three members Nadal and Djokovic.

Together, the trio of tennis legends pushed the sport to new heights, breaking record after record and winning 20+ Grand Slam titles each. The Spaniard and the Serb have 22 and 23 respectively, and there is a strong chance that Djokovic could still win several more.

Recently, former Top 10 player Petkovic revealed that she thinks Federer would have retired much earlier than he did if it hadn't been for this rivalry.

As the oldest member of the Big Three, Federer was the first one to break Pete Sampras' record of 14 Grand Slam titles. This impressive feat was achieved at Wimbledon in 2009, where Federer defeated Andy Roddick in five sets.

Now, Petkovic has said that she doesn't think Federer would have been motivated to continue playing for much longer after this had it not been for Nadal and Djokovic snapping at his heels.

"If we go back to 2009, when Roger Federer broke Sampras' number. If Rafa Nadal & Novak Djokovic hadn't appeared, Roger would've stopped at 17 Slams. 100%. We would've never seen these numbers," she said.

Regardless of whether or not Petkovic's observations would have been correct in an alternate universe without Nadal and Djokovic, it is certainly true that the rivalry between the three players pushed the sport forward in multiple ways.

Not only have all three continually broken the record for most Grand Slam titles won in men's singles, but their matches against each other were some of the greatest in tennis history. The two most significant ones were Djokovic and Nadal's head-to-head at the 2012 Australian Open final, and Federer and Nadal's face-off at the 2008 Wimbledon final.