World No. 1 Rafael Nadal is not exactly sure how he, Roger Federer and Novak Djokovic are continuing to dominate the sport of tennis even in their thirties.

From the beginning of 2017, it was Nadal, 32, and Federer, 36, who both experienced career resurgences as since then, they have won a combined 20 titles which includes six Grand Slam triumphs.

The latest player to have a career resurgence is Djokovic, 31, who after an injury-plagued 2017, improved dramatically this year, culminating in his Wimbledon triumph earlier this month for his 13th Grand Slam victory and first major title since 2016.

With the trio now boasting a combined 50 Grand Slam triumphs, including the last seven that have taken place, it has begged the question as to why the younger generation aren't challenging for more major honors.

There are just three players under the age of 24 present in the top 20 and the arguably one of the most promising of them all in No. 3-ranked Alexander Zverev, 21, has drastically underperformed in the Grand Slam events with his best performance being a quarterfinal exit at the French Open earlier this year.

Dominic Thiem, 24, reached the final of the French Open this year but other than that, the last two years have more or less seen a lack of the new generation challenging the old guard.

Nadal believes there can only be two reasons as to why this is the case with the sport right now.

"There are two options to explain the fact that three players are dominating the [tennis] circuit for so many years, and that we are in the top positions in the ranking for so many years," Nadal explained, as per the Express. "Either we have been special, or the emerging players have not been special enough."

"I cannot say which is correct. A generation with special players [is coming], either because they will be better than us in a short time, or because of our age," he said.

Nadal had a chance to win his 18th Grand Slam title at Wimbledon, especially after Federer's shock exit in the quarterfinals to eventual finalist Kevin Anderson. However, he would lose a thrilling five-set semifinal battle with Djokovic, who looked like the player who won four Grand Slams in a row back in 2016.

Despite the missed opportunity, Nadal is just happy to be fit and competitive, considering the injury problems he has suffered since the end of last year.

"My goal has never been to win everything," Nadal said, adding that he prefers "to be competitive every week, and if I win, all the better."

"At this point in my career, winning is the essence of the sport, but competing well and enjoying at highest level is what makes me really happy," he added.

Both Nadal and Djokovic are expected to return to action at the Rogers Cup which takes place from Aug. 6-12 next month in Toronto, Canada. Federer will miss out after withdrawing due to scheduling reasons.