RIO DE JANEIRO • The highly anticipated showdown between Sun Yang and Mack Horton in the men's 1,500m freestyle final will have to wait another day, after the Chinese swimmer, who was struggling with illness, failed to progress from his heat on Friday.

Sun, who was earlier in these Games branded a "drug cheat" by Horton, finished 16th overall in qualifying and even failed to break the 15-minute mark.

Horton eased through the same race and dismissed the importance of Sun's premature exit.

"It doesn't really matter if he is there or not to be honest," the Australian 400m gold medallist said.

Sun said he fell ill following his gold medal-winning swim in the 200m freestyle, and his malaise showed on Friday when he could only manage 15min 1.97sec, a time more than half a minute off the benchmark he set in London.

The outgoing Olympic champion had boasted last week that he was the "king of 1,500m", but admitted his efforts in bouncing back from the disappointment of losing out to Horton in the 400m freestyle had taken their toll in the 200m race.

"I was quite sick right after the 200m. I then took six antibiotic pills every day and that made a difference," Sun said.

"I didn't think my body condition had declined so much after the 200m but I had swum 1min 44 sec, something I'd never done before, so that was really intense."

Sun added that he had not been helped by the effects of jet lag since arriving in Rio.

"I basically haven't had any personal time - eating, training and doing physical therapy before Rio. I spent at least two hours every night and even here in Rio, I was being treated to two or three in the morning," he said.

"It's been really hard for me to fall asleep every night. After spending time in the US, and then coming to Brazil, my whole biological body clock has been messed up.

"Often when it's three or four in the morning, I've been wide awake staring at the ceiling."

Sun will leave the Games with one gold and one silver and a mixed bag of emotions.

"I'm a bit happy and a bit sad and there are lots of things I can reflect upon later," he said.

THE GUARDIAN, AGENCE FRANCE-PRESSE