The Bayern Munich man was the first player to be sent off in the tournament when he pushed Jerko Leko in the Group B defeat to Slaven Bilic's men, which meant he was suspended for the 1-0 win over Austria on Monday.

"I did make a mistake against Croatia and I know that, but I will try and play my game and hope to make some positive contributions to help the team win this game," he said.

"I think if we do win this game, then I will have played my part to help.

"We showed against Poland what we are capable of, but we also know that we can do even more and that is our biggest strength.

"Hopefully we can build on our good games, like away at the Czech Republic in the qualifiers. That game has got to be our benchmark for tomorrow."

The two nations met in the third-place play-off at the 2006 World Cup when two goals from Schweinsteiger helped Germany to a comfortable 3-1 victory, but the 23-year-old knows tomorrow's game is going to be much different.

"It is a new game and Portugal have changed a lot from then and it will be a lot more difficult than in 2006," he said.

"They are more mature and, for me, they are the strongest team at Euro 2008.

"I expect it to be a very difficult game for us."

Portugal, having won their first two group games, rested most of their team in the defeat to Switzerland, so many of Luiz Felipe Scolari's men have had a full week to prepare for the last-eight showdown.

"Portugal have had one day more to recover than us, but that should not play a role," Schweinsteiger added.

"We have got to put our foot down from the very beginning.

"I don't think we have to be fearful in any way. It is a new game, a knockout game, and we have the right attitude for it.

"They are the big favourites for the title and, except for their last game, they have played excellently and it will be very hard to beat them."

Coach Joachim Low could be forced to sit in the stands following his dismissal from the bench against Austria, with UEFA set to decide the sanction today.

Torsten Frings remains a major injury worry for Germany as he was diagnosed with a broken rib on Tuesday afternoon. He will try to take part in Germany's final training session but Thomas Hitzlsperger is on standby to replace him.

Portugal winger Cristiano Ronaldo has warned his team-mates there is no margin for error against the Germans.

"We know that we can't make any mistakes and that we will have to concentrate from the first moment to the last if we're going to get what we want," he said.

"You have to respect Germany. They are always a very dangerous team, but we have threats on our side too."

Triumph in Austria and Switzerland would cap a stunning season for the Manchester United star, but he insists a victory for Portugal is all that matters.

"It's a source of great pride to me that my career keeps getting better," said Ronaldo.

"I'm part of a great national team as well as a great club side.

"I hope I can have an important role in the game but the team is more important. Small details make the difference in big games and I hope those will be on our side. Winning is the most important thing."