The co-hosts claimed a surprise 2-0 victory over the United Arab Emirates in their Group B opener on Sunday and know three points against Dzemaludin Musovic's Asian Games gold medalists, who shared a 1-1 draw with Japan on Monday, will secure a place in the last eight.

But a draw at the My Dinh National Stadium would leave Vietnam needing points against Japan in the final group game, and after the defending champions dropped points against Musovic's side, Riedl is well aware Ivica Osim's side will be no pushovers.

"We never expected to be top of the group at this stage, maybe another team but not Vietnam. We were a little bit lucky in the first match, but we also played well; luck and playing well together means success," he said.

"We are used to playing in front of large crowds at home, but we have the same problem when we play away. If can affect you sometimes. But when you have a full stadium it can help you, it can even help the other team.

"The game is very important for us, maybe more than Qatar, because we have to play Japan in the last game.

"But there is no pressure on us. We came into the group as the outsiders, but now we have one win. We know a win will send us through, a draw gives us a chance while a defeat also leaves us with a chance."

Riedl, who has no injury concerns ahead of the game, does admit he does not know what to expect from Qatar after they switched between strategies against Japan, often leaving striker Sebastian Quintana to lead the attack as a lone frontman

He revealed may consider changes in tactics or personnel to deal with the Uruguayan-born frontman, who he sees as the UAE's main threat following his tireless efforts against Japan.

Qatar coach Musovic believes the UAE underestimated the strength of Vietnam, a mistake his side will not be repeating in their AFC Asian Cup Group B meeting, and insists all four teams in the group now have no secrets following the first round of fixtures.

Qatar will be without suspended striker Hussain Yaser following his stoppage time dismissal against Japan, with Seyd Bechir be set for a place alongside Sebastian Quintana in attack.

"It was a good thing for us that we did not have to play the first game against Vietnam. We have managed to collect a lot of information from their game against the Emirates and the whole team know they must not make the same mistakes as the Emirates team," he said.

"The Emirates team did not prepare and did not take the game against Vietnam seriously. The coach and the technical staff would have stressed how much quality Vietnam have, but the players did not accept this and they believed they would have an easy game.

"They controlled the game for 30 minutes but after that their performance and concentration went down. After half-time Vietnam dominated the game. Players must play for the entire game to get a positive result."