South Korea's Son Heung-min said he was blocking out thoughts of being tired as he slogs it out at the Asian Cup on the back of a frantic spell of football in recent months.

The World Cup, Asian Games and Premier League have all taken their toll, and talk of fatigue drew a rueful look from Son after South Korea were taken to extra time in their 2-1 last-16 win over Bahrain.

"It's about mentality I think," the Tottenham Hotspur player said, grimacing and rubbing the back of his head. "If you think you're tired, you get tired.

"After the game I feel tired of course but still I try to recover as quickly as possible and play again. In three days I can recover.

"It's the same when I'm playing with Tottenham as well. I have to recover as quick as possible and look forward to play."

Coach Paulo Bento has voiced concerns over the condition of his captain, who is leading South Korea's charge for a first Asian Cup title in 59 years.

Before arriving in the United Arab Emirates, Son, 26, played in 12 matches in a little over a month for Spurs, who have lost both Harry Kane and Dele Alli to injury in recent days.

Injuries have also become an increasing problem for the Taeguk Warriors, whose hopes took a knock when they lost Newcastle midfielder Ki Sung-yeung to a hamstring injury.

"I think he's a big loss," Son said of Ki, whose number 16 shirt was brandished by his teammates after Kim Jin-su's extra-time winner in Dubai.

"He's one of the best players in the squad of course. He's a big loss and someone else will have to be ready to step up and show what they can do."

Bento admitted injury absences had robbed South Korea of some ideas in attack, and they looked flat and vulnerable at times against a Bahrain team who packed the defence.

"In the positions where we can refresh the team a little bit in terms of attack, we have difficulties," Bento said after the laboured win over Bahrain's part-timers.

"But now we need to find solutions because on the 25th we will play again. So it's not an excuse, it's what we have in this moment."

Last year Son starred -- and scored -- as South Korea knocked defending champions Germany out of the World Cup, and he also led his country to victory at the Asian Games, a title which earned him an exemption from military service.

After playing 209 minutes in two games since arriving for South Korea's final group fixture, Son will now need to lift himself again for Friday's quarter-final against Qatar.

But despite being on the receiving end of some rough challenges, including a boot to the head, he said he didn't feel he was being singled out by opposition teams.

"No, I've never been targeted. But sometimes it's difficult when you play with such a team who play with 10 players in defence and you can't find any space," he said.

"Everyone can be a target, I don't worry about this. I have to learn from this. We should play better than this game."

Son added: "We're looking forward to playing the quarter-final. Of course it's going to be a very tough game, like today. But we're looking forward.

"We got the result, of course the performance wasn't great but sometimes you take the result."