Sunderland boss Ricky Sbragia believes Porto surprised Manchester United by attacking from the offset at Old Trafford.
Sbragia watched from the stands as Villarreal added to their early break through with a late equaliser at Old Trafford.
And, with United making the trip to the Stadium of Light this weekend, the Scot will be hoping his side can employ similar tactics.
No stranger to United's play having coached the reserve team before taking charge of Sunderland, Sbragia admits he will be taking nothing for granted against Sir Alex Ferguson's side despite their recent dip in form.
"Porto surprised them," said Sbragia. "They attacked them early doors, got the goal and had a couple of chances and they made the game big as well.
"They worked extremely hard against Manchester United, but I felt the longer the game went on, Manchester United started taking charge of it.
"They got back to 2-1 and the game, for me, would have been over. But credit to Porto, they came back and scored late on.
"But they can change it around. You look at their bench last night and they have got some good players there as well who they can bring in."
United's defence has been questionable in recent outings, though they did recover well against Aston Villa after suffering back-to-back defeats against Liverpool and Fulham.
"They are a top team and we know it's going to be very difficult," added Sbragia.
"We watched them against Porto last night and watched them against Villa,
and they are a good team. They are an attacking team, they score goals.
"You just don't know what sort of team they are going to put out on Saturday, but we know it's going to be a very difficult game."