Roger Federer and Rafael Nadal
Roger Federer and Rafael Nadal have defied their age since returning from injury layoffs last year. Pictured: Roger Federer of Switzerland (L) is congratulated by Rafael Nadal of Spain after their men's singles final match at the Shanghai Masters tennis tournament in Shanghai, Oct. 15, 2017. CHANDAN KHANNA/AFP/Getty Images

Roger Federer and Rafael Nadal can continue playing tennis at the highest level even in their forties, according to the latter's coach Carlos Moya.

Federer, 36, and Nadal, 31, both experienced career resurgences in 2017 after returning from long injury layoffs as they won a combined 13 titles during the calendar year with the Spaniard ending the year as the world No. 1.

They also shared the four Grand Slams between themselves as Federer's victory in the Australian Open was his first major title since 2012 while Nadal's record-breaking 10th French Open crown was his first major title since 2014.

The legendary duo not only defied injuries but their age as well as not many expected them to dominate the 2017 season, especially after previous years where Novak Djokovic and Andy Murray had dominated.

Federer's success continued in 2018 as he won the Australian Open once again before making history and overtaking Nadal, who injured himself in Melbourne, to become the oldest world number one in tennis en route to winning the Rotterdam Open in February.

The Swiss ace would, however, lose his spot at the top of the rankings to Nadal this month after a surprise opening round defeat at the Miami Open which was preceded by a loss to Juan Martin del Potro at the Indian Wells final.

With a change at the top of the rankings likely to occur again if Nadal is unable to emulate his clay-court campaign from last year, Moya heaped praise on the pair for being able to remain at the top of the rankings at an age considered one for retirement in the past.

"Until Saturday, he [Federer] was the world No. 1 at 36: it seems [like] tennis fantasy, no?" Moya was quoted as saying on Tennis World USA. "At my time, in the 90s, at his age, we were retired for six or seven years but Roger is phenomenal. Rafa as well, at the top of the rankings as a 31-year-old, it's not bad! Tennis changed: I wouldn't be surprised to see them still there in their forties."

Nadal is expected to feature during the clay swing, having not played competitively since pulling out of the Australian Open back in January. The Manacor native was to return at the Mexican Open in Acapulco last month but then withdrew on the day of his match after an injury during a training session.

"Before that [injury in training], it was all perfect," Moya explained. "He had the same problem as at the Australian Open. We tried to figure out why it happened: was it a setback? A chronic issue? Injuries are always the worst loss for a tennis player: they keep you away, detracting your confidence. But now he is on the court in Manacor."

"No I wasn't [worried]. I was more worried about the knee injury last year. When Rafa's joints are in the middle, then I get panicked. But this time nope: it's a thigh muscle. And then the past consoles me. Now we have to find a balance: fewer hours on court, with more quality. In the matches, the strategy is to be more aggressive to shorten points," he said.

Nadal was recently named in Spain's Davis Cup squad and could feature in the quarterfinals against Germany which take place in Valencia from April 6-8 — a couple of days before the Monte-Carlo Masters.