Speaking to Sky Sports, Ferguson said, "Porto are a very aggressive team, especially on their own ground. The introduction of Brazilian and Argentinean players into their team has given them both a flair and toughness that is very much in evidence when they play at home.

"They can have their off days, though. They lost on their own ground to Dynamo Kyiv in the group stages earlier this season and were also well beaten by Arsenal at the Emirates."

In England, Sir Alex has masterminded some good success over Porto but is yet to beat the Azuis e Brancos on their own patch.

He added, "We have had mixed fortunes against them in the past. I recall, in the time of Eric Cantona, when we beat them 4-0 at Old Trafford and then drew 0-0 in Portugal.

"The most recent experience was not so successful, when we came up against an emerging Jose Mourinho.

"They are a different proposition now.”