Rafael Nadal's lingering foot injury which forced him from the ATP Toronto Masters on Tuesday may affect his US Open future.

The Spanish world number three pulled out in Canada a day before what would have been his opening match against 50th-ranked South African Lloyd Harris, who defeated him last week in the third round in Washington.

The left foot injury which Nadal says he has carried since around 2005 had bothered him since Roland Garros and now appears to threaten his chances for the final Grand Slam of the season starting on August 30 in New York.

"I've had this issue for a couple of months," said Spain's Nadal, who skipped both Wimbledon and the Tokyo Olympics after a French Open semi-final loss to Novak Djokovic.

"Of course it is not a happy situation after all the success that I had here in Canada," said the 35-year-old, who has won five Canadian titles.

"I need to go back (to Mallorca) and try to find a way to be better again. "The most important thing is to enjoy playing tennis," he said. "With this pain, I'm not able to enjoy (playing)."

After aggravating his foot injury in a second-round win over Jack Sock last week, Nadal said after his loss to Harris that it had improved.

But on Tuesday he said it hindered him too much to allow him to be competitive in Toronto.

Spain's Rafael Nadal is out of the ATP Toronto Masters with a nagging foot injury
Spain's Rafael Nadal is out of the ATP Toronto Masters with a nagging foot injury GETTY IMAGES NORTH AMERICA / Mitchell Layton

"I don't believe that I had chances to fight (in the tournament)," said Nadal, who had a first-round bye.

The injury looks likely to lead to a withdrawal from next week's Masters 1000 in Cincinnati, leaving Nadal's US Open participation in question.

Nadal, who holds 20 Grand Slam singles titles alongside Roger Federer and Novak Djokovic, has dealt with physical problems throughout his career.

He is well-versed in treatment for knee problems, which he has always managed to overcome throughout his career.

Nadal has little left to prove at age 35 and will surely take as much time as needed to sort out his foot trouble.

"The most important thing is to enjoy playing tennis. With this pain, I'm not able to enjoy," he said.

"I've (had this) pain the last couple of months. I wanted to try (to play) even like this."

Officials said the second-seeded five-time champion will be replaced in the draw by fellow Spaniard Feliciano Lopez.