TOKYO - Joseph Schooling does not need anyone to tell him - he knows his performances at the Tokyo Olympics were not up to scratch.

On Thursday night, Singapore's only Olympic champion relinquished his 100m butterfly title after he failed to progress out of the heats at the Tokyo Aquatics Centre.

He clocked 53.12 seconds to finish last in his heat and place 44th out of the field of 55. His time was almost three seconds slower than the 50.39sec that helped him win the gold medal at the Rio Games five years ago.

In the 100m freestyle heats on Tuesday, he clocked 48.27sec - about 1.5 seconds off his national record - and placed 39th out of the 70-strong field.

Hands on hips, he said last night: "It's a very disappointing performance overall, but there's always another one. It's not going to end like this."

He added that he felt his time did not reflect the progress he had made with long-time coach Sergio Lopez this year in preparation for Tokyo.

"Sometimes that's how it is," he said. "It's hard to swallow and digest. But at the same time, I live to fight another day.

"And I sure as hell don't want it (his career) to end like this."

The 26-year-old reiterated that message - that he was not ready to throw in the towel - a total of four times during his race post-mortem with members of the media at the mixed zone.

As he dissected his race, the TV behind him showed American Caeleb Dressel, the world record holder, clocking 50.39sec in his own heat to equal the Olympic record Schooling had set in Rio. Dressel was the quickest of the 16 swimmers to advance to today's semi-finals.

Swimming in the fifth of eight heats, Schooling was slow off the blocks and was last in his race even before the halfway point.

Teammate Quah Zheng Wen also missed the cut after clocking 52.39sec to finish fourth in heat four. He finished 34th overall.

Lopez, a Spaniard, told The Straits Times last night that Schooling "hasn't been feeling powerful" in training and it was evident in his two races in Tokyo.

"It's an obvious thing… (but) I'm not sure what has happened."

Schooling said he felt "a bit off" and "flat" on the blocks. But he insisted that it was "not a fitness issue".

Eyebrows furrowed, he said: "Usually when you get up for a big race like this, your heart is pumping, the adrenaline is flowing… but this felt like I was boxing 12 rounds and starting the 11th."

When it was suggested a radical change to his training methods might be the remedy, he disagreed and said "it's not a complete wash".

"It's just finding that spark, you know?" he said. "That can be one realisation or a month or two of work. I don't know what it is but at the same time, I know it's (his career) not going to end like that."

Lopez, who said the first thing he did after Schooling's race was to give his swimmer a hug, said the Singaporean "has reacted very well" from a tough outing but added he would benefit from time away from the pool.

"Right now, Jo needs to take a little break, refocus, and keep moving forward," he said.

Asked if he had any regrets about how his Tokyo campaign had unfurled, Schooling shook his head and said: "No, I'm really disappointed, I wanted to be a lot better and go way, way faster and be in contention and on the podium… But, no regrets."

Lopez said that he was "sad for Jo and sad for Singapore swimming" but added: "We've been in enough competitions at world-class level that you have some good ones and some bad ones, and we have just got to keep moving ahead."

The coach said he already has one eye on the 2022 Asian Games in Hangzhou in 13 months' time as a possible stage for a Schooling comeback. The Singaporean is a two-time 100m fly defending champion at the Asiad, having won gold in 2014 and 2018.

"This (failure) is part of life," added Lopez. "One of the things I told Jo a while back is that he is an Olympic champ, and nobody can take that away from him.

"Singapore should be super proud of having a kid - now a man - who has done Singapore proud and still wants to do the country proud."

As Schooling himself defiantly insisted last night, Tokyo, bitter as it is, is not the end.