Rafael Nadal has said injuries are part and parcel of modern tennis, insisting he is far from finished after a knee injury forced him to retire midway during the US Open 2018 semi-final against Juan Martin del Potro on Friday, September 7.

Nadal, whose career has been plagued by injuries, especially the recurring knee issues, said he was in too much pain to continue the semi-final, in which he was trailing 6-7(3), 2-6.

The world number one had headed into the tie after a marathon quarter-final tie against Dominic Thiem, who pushed the Spaniard to the limits on a humid night in New York. He was also made to work hard for his Round of 16 win over Karen Khachanov that came in four sets on a similarly energy-sapping evening in the city.

Nadal seemingly looked uncomfortable on Friday even as del Potro brought out his powerful game and hit winners at will at the Arthur Ashe Stadium.

"All my career everybody says that because of my style I will have a short career. I am still here. I am still here because I love what I'm doing. I still have the passion for the game," Nadal told the media on Friday.

"I'm going to keep fighting and working hard to keep enjoying this tour and keep having chances to compete at the highest level. So that's all.

Rafael Nadal
Nadal vows to fightback after latest injury setback.Al Bello/Getty Images

"I know the things are going the right way. I am playing well. I am enjoying (being) on the court. I am having a lot of success.

"I am very competitive at the age of 32. A lot of people in this (media interview) room, including myself, never will think that at the age of 32 I will be here fighting for titles, fighting for the first position of the rankings."

Sure it will not be six months: Nadal

Rafeal Nadal
Rafael Nadal retired after the completion of second set of his US Open semi-final on Friday.Al Bello/Getty Images

The 17-time Grand Slam champion, who had retired from the Australian Open quarter-final with a hip injury, said he is suffering from tendonitis — a knee issue that had kept him out of the game for eight months between 2012 and 2013.

Nonetheless, Nadal has ruled out a long injury layoff and that the experience of dealing with knee issues will help him overcome his latest injury.

"I cannot compare the knee with other times as the pain is always very similar. This time it was a little bit more aggressive with my movement," Nadal added.

"I know what I have. It is a similar thing to always so it is about good treatment.

"It is not an injury that tells you, 'three weeks off, you are back. Six months off you are back.' I know what I have to do to be better as soon as possible.

"I am sure it will not be six months off of course, I was just making a comparison."

Meanwhile, former champion del Potro received the ticket to only his second US Open final. He will be facing an in-form Novak Djokovic, who outclassed Kei Nishikori in straight sets in the second-semi-final, on Sunday evening.