Nemanja Vidic has told his Manchester United team-mates to show their mental strength to avoid an early exit from the UEFA Champions League.
Porto's shock 2-2 draw with United at Old Trafford on Tuesday has left Sir Alex Ferguson's men the uphill task ahead of next week's trip to Portugal and Vidic is aware of the challenge ahead.
The Serbian defender is aware that no Premier League side has ever beaten Porto at the Estadio do Dragao and United will almost certainly need to end that record after handing their Portuguese opponents the away-goals advantage.
Vidic, a strong candidate for player of the season, believes injuries to key players and United's on-going quest for five trophies may have knocked the Champions League holders out of their stride.
The 27-year-old, whose central defensive partner Rio Ferdinand is likely still to be missing next week, said: "Now we have a hard job to do. No English team has won in Porto before so that's a big challenge for us.
"If you look at the last four games then obviously we haven't played as we did in the 10 games before that. We definitely need to get back on the right road, we need to get back that mentality.
"Maybe we need to work on our defence because in the last few games we have conceded too many goals.
"I don't think it's a case of players not having the confidence.
"But maybe we've had so many games and also we've had players injured - at this stage of the season you need all your players to be ready to play the games.
"We need to prepare as best we can, we need some players back from injuries and we can make it through."
Vidic warned however that it could be a mistake for United to out with all guns blazing in Portugal.
"We can't go there stupid and go into attack with all our guns," he said. "We need to be clever.
"They have some good players, they have quick players up front and they are going to be waiting for our mistakes and ready to score one goal again.
"We need to be clever and hopefully we can go into the semi-finals."
Vidic also insisted United had not made the mistake of underrating their opponents.
He said: "When we watched the videos we saw definitely they have the quality. Even before the video I knew they were a good team.
"They have shown over the years that in Porto they never lose.
"It's hard to win there. If you look at Arsenal and how they played them and against Chelsea and you see it's a hard game against them."
Meanwhile, United midfielder Michael Carrick said the team should not be too downhearted by the draw.
"We shouldn't be too down, we are still involved and still have a very good chance of going through," said Carrick.
"They are a tough side but we know what we have to do. We are confident that we can beat anyone on our day and we believe we will win, we will give it our best shot.
"They are a good team, I'm not saying that's anything to worry about - that's what you expect in the competition at this stage.
"This result has made it harder than we would have liked but if you want to win this trophy you have to overcome things like this and hopefully we can to that."
Carrick believes United need to defend as a team to return to the form that saw them play 14 consecutive Premier League matches without conceding a goal.
"We were on an unbelievable run and things have changed there and we need to put that right and not having to score two, three or four goals ourselves to win matches," he said.
"We need to defend as a team and put it right and I'm sure that we will.
"We have been aware that things have not been going right and we are trying to put that right."