(CNN) -- Cristiano Ronaldo has warned holders Manchester United that Champions League quarterfinal opponents Porto will be no pushovers, ahead of Tuesday's first leg clash at Old Trafford.
Ronaldo is confident holders United will see off Porto's challenge of two legs and reach the semis.
"Porto are a very good team," said Portugal's World Player of the Year. "They are top of the league back home, ahead of Sporting Lisbon and Benfica and we know how strong they can be."
But Ronaldo, who scored twice in the dramatic 3-2 win over Aston Villa that sent United back to the top of the Premier League, is confident enough to predict that United will reach the last four
"The good thing is we have two games against them and I feel that will be enough to get us through," he said.
United are odds-on favorites to reach a third successive semifinal, but manager Alex Ferguson also respects a side that finished above Arsenal in the group phase and defeated highly-rated Atletico Madrid on away goals in the last round.
"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, 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."
Brazil forward Hulk, man-of-the-match as Porto extended their unbeaten league run to 16 games at the weekend, provides a physical threat with strike partner Lisandro Lopez equally capable of causing United damage.
Ferguson feels the last-gasp win over Villa can kick-start their push for glory after it had appeared United's mini-slump was about to turn into a full-blown crisis.
They were trailing 2-1 when Ronaldo equalised. Then, in the second minute of stoppage time, debutant Federico Macheda curled home a magnificent winner to send United into ecstasy.
"The winner was one of those incredible moments you probably only get at this club and it could well galvanise the club," said Ferguson who keeps the 17-year-old in his squad against Porto.
United will be bolstered by the return of Wayne Rooney, Nemanja Vidic and Paul Scholes from suspension, but Rio Ferdinand is still sidelined by a groin injury.