World number one Rafael Nadal responded to a simmering debate about the amount of tennis the top stars play, saying: “We are not 20 years old any more.”

The 31-year-old Spaniard reached the final of the China Open on Saturday, seeing off Bulgaria's Grigor Dimitrov in three sets.

Despite his advancing years Nadal is enjoying a stellar season following a catalogue of injuries in previous seasons, winning five titles including the US Open and French Open.

But many of his rivals are suffering injury or fatigue as the season approaches its climax, with Novak Djokovic, Stan Wawrinka, China Open defending champion Andy Murray and Japanese star Kei Nishikori all missing.

However, the oldest of the lot, Roger Federer, is set to compete in Shanghai next week and Nadal refused to add his powerful voice to those demanding fewer tournaments.

“When I have been in that position (injured), I don't remember the people talking that much about these things,” Nadal said after defeating the 26-year-old Dimitrov in their semi-final.

“The problem now is there is a couple of players (injured), it's a coincidence, first thing.

“Second thing, we cannot forget that we are not 20 years old any more.

“It is true that the calendar is tough, but at the same time it is true that Federer has 36 years, I think, I have 31, Novak 30, Andy 30, Nishikori, I don't know, 27.

“It is normal that at some point these kind of players that are playing a lot of matches and a lot of years in a row, at some point they have some problems."