South Korea boss Uli Stielike fears a fever could sweep through his squad and hamper his efforts to make dramatic improvements after two stuttering performances so far.

The Taeguk Warriors are safely into the quarter-finals despite labouring to unconvincing 1-0 wins against lowly Oman and Kuwait which left the German seriously worried.

"I see two good things," he said. "First of all we have six points from two games but the second good thing is that we are out of the role of the favourites because with football like this you cannot win the tournament.

"That has to be clear for ourselves, in the mind of each player that with a performance like today you cannot go far in this tournament."

South Korea face their first big test on Saturday, when they take on in-form hosts Australia for the potentially valuable prize of finishing top in Group A.

But they will first have to recover from injuries and also a virus which forced Bayer Leverkusen star Son Heung-Min, Koo Ja-Cheol and goalkeeper Kim Jin-Hyeon out of the Kuwait game.

Together with Lee Chung-Yong's hairline leg fracture, and knocks to right-back Kim Chang-Soo and forward Cho Young-Cheol, Stielike made seven changes to his starting line-up for the Kuwait game.

"Maybe tomorrow more players will be sick. If you have fevers in a group you don't know who will be affected next," he said late on Tuesday. "The fever could attack any player at any time so we don't know."

He added: "Our main objective now is the recuperation of the players. We'll have to see over the next few days which players will be 100 percent for the game.

"We have to go for first place in the group but against Australia if we play the same way we have no chance."

South Korea are bidding for their first Asian Cup title in 55 years and were one of the pre-tournament favourites.

But they face added pressure after a poor World Cup in Brazil last year prompted coach Hong Myung-Bo's resignation and the surprise appointment of the unheralded Stielike.

"I think our main problem is the mentality," said Stielike. "If you don't live in Seoul, you don't know the expectations on this team. Everyone thinks against Oman and Kuwait that you go out and walk and you win four or five zero.

"But now this has happened, we take away the pressure the players have with them. When you see the easy mistakes we made today, like control of the ball and passing over two, three metres.

"The players can do that with their eyes closed in training but on the field they have so much pressure, they think 'I cannot make this mistake' and then they make those mistakes," he added.