Quins' Heineken Cup ambitions go on the line when they tackle four-time tournament winners Toulouse in France.
After losing 21-10 at home to the competition heavyweights and Pool Six favourites last week, Quins will have little realistic chance of reaching the knockout phase if they suffer another defeat.
But O'Shea is relishing the task that awaits the Aviva Premiership leaders, whose 14-match unbeaten record this season came to an end eight days ago.
"They are four-time European champions with 24 internationals in their squad. They are the Barcelona of European rugby," O'Shea said.
"We are under no illusions. They were very physical (last Friday), but this team learns very quickly.
"We want to put our game on the pitch, enjoy playing against them and we will see where it takes us. We showed some resolve, but we didn't think we did ourselves justice last Friday.
"We will become a better team for what happened.
"The boys had a few days off and they have come back in with a massive intensity. We will have a side who will want to go out with a huge intensity and physicality this weekend.
"We are playing against the greatest side in European history, and if we can't learn from that then we are in the wrong game."
Quins were largely undone by Toulouse's ferocious intensity at the breakdown, where flanker Thierry Dusautoir and number eight Louis Picamoles delivered colossal displays, although Quins never shirked from their task.
O'Shea added "If you put these boys out for a game of tiddlywinks they will want to win. That is the competitive nature.
"Last Friday was a one-score game, then they got the break and finished the try. The pass was five yards forward, but those things happen in games.
"You have some ties in the Heineken Cup that make up the numbers, but this game last week was not one of them. It was two unbeaten teams going head to head.
"Yes, we didn't win at home, which is bad when it comes to the Heineken Cup and it has put us under pressure. But I would prefer us to be playing those games because we learn something and we will become a better side."
Quins' degree of difficulty, though, has increased through losing key forwards Joe Marler and Maurie Fa'asavalu through injury. Prop Mark Lambert replaces Marler, with flanker Will Skinner taking over from Fa'asavalu.
Toulouse, meanwhile, showcase their enviable strength by naming another powerful line-up, with French internationals Picamoles and Jean-Baptiste Poux on the bench alongside Australia's World Cup scrum-half Luke Burgess.
Northampton, Heineken Cup runners-up last season, have little chance of qualifying from Pool One following successive losses to Munster, the Scarlets and Castres.
Saints meet Castres at Franklin's Gardens and rugby director Jim Mallinder knows his players must show a marked improvement.
"We had good attacking intent and scored some good tries last week (against Castres)," Mallinder said.
"But we didn't keep hold of the ball well enough and we conceded too many penalties. That is something we are going to have to put right this weekend, along with our defence.
"The players want to prove a point. There are no 'nothing' games at this level and there has been a good response in training this week.
"You are representing the club every time you pull on the shirt, and I expect that the team will come out on Sunday fully-motivated for what will be a tough challenge."
Pool One leaders Munster host the Scarlets as firm favourites to extend their unbeaten record in Europe this season, although the Welsh team are not out of contention despite suffering a 17-14 home defeat to the Irish side last Saturday.
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