McCartney secured a bronze medal at the Rio 2016 Olympics, but has since been troubled by an Achilles problem.

The injury disrupted preparations for the Gold Coast 2018 Commonwealth Games, where McCartney won a silver medal, before forcing her to miss the World Athletics Championships in Doha last year.

McCartney told the World Athletics-backed magazine Spikes that the injury could be caused by an autoimmune condition, based on blood tests and her family's medical history.

The 23-year-old has said the postponement of Tokyo 2020, due to coronavirus crisis, could offer her a chance to qualify and prepare for the Games.

"Before they got postponed, it was going to be a real push to qualify, but I was fairly at peace that if I didn’t make it, that was just the way it goes," McCartney told Spikes.

"But because I’m reasonably young, another year can’t be a bad thing.

"It gives me a chance to get a real base training going.

"If I make it to Tokyo, I know I’ll have a different mindset to what I had in Rio.

"That’s the thing about injuries, they leave you with a certain wisdom.

"There’s no more taking it for granted, I’m grateful that I get to do this."

McCartney needs to clear a height of 4.70 metres to achieve automatic qualification for Tokyo 2020.

The New Zealand star has a personal best of 4.94m.

McCartney told Radio New Zealand she is currently resting her Achilles after the injury flared up during an Athletics New Zealand training camp in June.

She added that adjustments to training, including the use of data to measure the load that she puts on each leg, have been made to help manage the injury.