He said: "We know it's going to be more difficult than in Manchester because United will arrive here looking for victory and needing goals.
"But the loss of Rio Ferdinand could be very important for them. Also, Cristiano Ronaldo wasn't decisive in the first leg and now he has to play under all the pressure and atmosphere our ground will generate, while knowing he could easily be going out of the competition.
"Obviously we have to avoid making errors, but we'll be happy to maintain our concentration and keep the game goalless. We have our own dreams.
"The first leg was the best match of my life.
"But as a team we showed why Porto are the Portuguese champions and that we can defeat anyone in Europe.
"United were not better than us at Old Trafford - and they know that.
"We can make it a very nervous night for them."