No English side has ever won there in European competition. But United simply have to win to guarantee a semi-final berth.
Former England star Scholes is convinced United can turn things around after the 2-2 draw at Old Trafford handed the Portuguese champions the advantage.
He said: “All we’ve got to do at Porto is win a football match.
“With the players we’ve got I’m sure we can do it.”
Scholes bagged the opener in United’s crucial win at Sunderland on Saturday with a wonderful glancing header from a Wayne Rooney cross.
Kenwyne Jones pulled struggling Sunderland level with half an hour to go. But teen sensation Federico Macheda once again slotted a late winner to keep the champions on track to retain their title.
Scholes believes the three points at Sunderland were a massive boost to United’s confidence ahead of Wednesday’s trip to Porto.
He said: “It’s always nice to get a win. It always boosts your confidence. I think we needed a little boost. That was a big win for us. Liverpool had won beforehand and Chelsea won as well. It doesn’t increase the pressure. You have to do your own job.”
Scholes raved about Italian wonderkid Macheda, 17, who followed up his sensational winner against Aston Villa last week with another at the Stadium of Light.
He added: “I think he scored with his first or second touch and he looks like a great goalscorer and, hopefully, there’s more to come.
“He’s a young lad but I’m sure the other boys will keep his feet on the ground.”
Keeper Ben Foster made his first Premier League start of the season on Saturday.
He revealed Macheda claimed he meant to side-foot Michael Carrick’s stray shot on target after deflecting in the winner seconds after coming on for Dimitar Berbatov.
But the England keeper has warned Macheda not to get carried away, otherwise Gary Neville will quickly slap him down to size.
Foster said: “He’s saying it was one of those intended deft touches into the corner. I don’t think the lads believed him!
“He’s quite level-headed and the lads would not let him get carried away.
“Gary Neville would quickly put his foot down on anything like that.”
obviously -.-