Dina Asher-Smith has withdrawn from the 200-metre race at Tokyo 2020 after struggling in the 100m semi-finals having torn her hamstring shortly before the Games.

A tearful Asher-Smith revealed the decision to pull out of an event where she is the reigning world champion as she reflected on a tough 100m outing.

The Briton, who took silver in the 100m at Doha 2019 and gold in the 200m, missed out on the final over the shorter distance with a semi time of 11.05 seconds, good enough for only third in her heat.

"Obviously I'm so disappointed to not make the final – it's Tokyo 2020, everything I've trained for for the last two years – but the last few weeks of my athletic life have been absolutely insane," Asher-Smith told BBC Sport.

She explained she had suffered a hamstring injury in the British Olympic trials final last month, prompting her withdrawal from events in Stockholm and Gateshead.

Asher-Smith expected she would not be able to travel to Tokyo.

"I was actually initially told it was a rupture and I'd need surgery and three to four months to get back," she said. "It's been a lot to deal with.

"Quite frankly, with that diagnosis, I couldn't have come to Tokyo. We had a statement ready to go.

"Thankfully, I went and got a second opinion and it was a misdiagnosis; it wasn't a rupture, it was a tear, but it was still attached, so we turned over every single stone to make sure I could stand on the line."

The 25-year-old still was not herself in the 100m, though, and was subsequently forced to make a call on Tuesday's 200m.

Asher-Smith had been the foremost British hope for a first athletics gold medal in an individual event since Jessica Ennis-Hill's 2012 heptathlon triumph.

"I am going to pull out of the 200m," she continued as the tears began. "As reigning world champion, I was in such good shape – you know that the Olympic champion is not much of a further step.

"Because of having three weeks off running, a week running slowly, I'm really proud to have been able to execute today and proud of doing everything I've done to this point.

"But when you're talking about the standard I know I'm capable of, there's plenty more championships for me to come and kill. We're in the middle of a four-to-five-year cycle.

"Yes, I've got a hamstring tear at the most inconvenient time but it doesn't change the calibre of athlete that I actually am.

"I know if I want to come and showcase that I need a few more weeks of power training to fill that gap that we had when I was trying to walk again, stretch my knee and trying to load my hamstring.

"John [Blackie, her coach] told me it's a no [for the 200m]. I would do it, because that's the kind of athlete that I am, but he's wiser than me. It's the Olympics, but there's another one."

Of her failure to make the 100m final, Asher-Smith said: "The most frustrating thing for me is that I was in really good shape. I was in the shape of my life.

"If you asked me six weeks ago, I was very confident I was going to win this because, being completely frank, every part of my race – my start, my transition and my finish – was better than some of the fastest women in the world.

"But when you have a hurdle like that, it's really hard to have a rejig."

Asher-Smith was part of a British team that took the bronze medal in the 4x100m at Rio 2016, also finishing fifth in the 200m.