Shaqiri warns to never write off Ronaldo ahead of knockout stages

"You cannot write off Cristiano, he is one of the best players in the world together with (Lionel) Messi," Shaqiri told reporters after training on Sunday.

"This guy can score any second, any minute, he has experience and everyone knows how important he is for Portugal and for his team," added the former Liverpool and Bayern Munich attacker, who scored in Switzerland's 3-2 win over Serbia on Friday which secured them a place in the knockout stage.

Ronaldo, who has been released by Manchester United after his controversial television interview, has scored once so far in this tournament, with a penalty in the opening group stage 3-2 win over Ghana.

But Shaqiri, who now plays in Major League Soccer with Chicago Fire, knows that regardless of Ronaldo's threat there are also plenty of other sources of danger from Portugal.

"We have to know also the other players because it is not only Ronaldo, they have very good players, young players who can make a big difference and we need to give really a very good performance because its knockout and anything can happen in the 95-100 minutes and we are looking forward to it," he said.

While Shaqiri is established as the main creative force in the Swiss side, he says the key to their chances of success is found in their ability as a collective.

"The key is to have a special performance from the whole team. There are no Cristianos in our team, we need to have the whole team to be successful. If everyone sticks together, everyone goes to their highest level of performance, I am sure we have a chance to go through," he said.

The two teams faced each other twice in the Nations League in June with Portugal enjoying a 4-0 win in Lisbon with Ronaldo scoring twice but then a week later, the Swiss gained revenge with a 1-0 win in Geneva.

But Shaqiri says the increased pressure of a World Cup knockout game makes past performances irrelevant.

"We know Portugal, we have played them many times in friendlies, in the Nations League, we lost some, we won some, for me everything is open, it is a knockout game but we know they are going to be a good team.

"We need a big, big performance, a special performance if we are going to go through," he said.