Fergie is wary of the quality the Portuguese side possess ahead of the first leg at Old Trafford on Tuesday.
“It would be stupid to think this is going to be easy,” said Ferguson.
“When teams are used to winning their domestic title, as Porto are in Portugal, you always feel they will play with great confidence.
“They have a lot of South Americans in their team as well, which gives them a great physical strength.
“By beating Atletico Madrid in the last round, Porto proved they will be hard to beat. Complacency does not come into it as far as we are concerned.
“We will be going at full throttle in order to get the result we want.”
