Barca have not won at Real Sociedad since May 2007, which will keep them on edge despite a 2-0 advantage from last week's first leg at Camp Nou.
Confidence will be with the La Liga champions though, after their spell off the summit of Spain's top flight was ended after just eight days courtesy of Sunday's 4-1 win at Sevilla.
Sociedad will not be giving hope of making the final and can look to last year's 3-2 win over Barcelona at Anoeta - after going 2-0 down - for inspiration.
Early efforts from Messi and Pedro looked to have set Barca on their way to an easy win but a goal from Gonzalo Castro and Gerard Pique's sending off rocked them.
Castro equalised six minutes after the defender's dismissal and Imanol Agirretxe popped up with a dramatic the winner in the 90th-minute.
He said: "On our part it is a tremendous motivation to be one step away from the final, but we know that it will be very difficult.
"We have never had a chance to play a final, and this is perhaps the only one.
"People believe (it can happen). There is a magical atmosphere at Anoeta and all the fans can help us so that Barca is not the usual Barca".
The majority of Carles Puyol's appearances this season have come in the Copa, but a back injury is likely to keep him out, while Neymar is doubtful despite training with the first-team squad this week as he recovers from a knee injury.
