The Frenchman confessed that he had tipped Cesare Prandelli's side for an early exit at the Euros, but has since been impressed with their "character and mentality"
Cesare Prandelli's men recorded a victory against Republic of Ireland and credible draws with both Spain and Croatia, to advance from Group C and set up a quarter-final tie with England.
However, Vieira confessed that he has been pleasantly surprised with the showing Italy have put in thus far, and feels that the last-eight clash with Roy Hodgson's side is too close to call.
|Italy ready for crunch clash
"I'll admit it: I thought Italy would go out in the first round," he told La Gazzetta dello Sport. "Instead, I saw a team with character and mentality that can play together. That's what it takes to win tournaments like this.
"That, and the quality of people like [Gianluigi] Buffon, [Andrea] Pirlo, [Daniele] De Rossi. I even had doubts about [Mario] Balotelli before the tournament.
"The England v Italy watch will be very balanced. And perhaps it will be a long game - I'm not ruling out penalties."
Speaking about the Three Lions, Vieira voiced his belief that Hodgson's charges have grown as the tournament went on, and that they have benefitted tactically during Fabio Capello's reign.
"Against France, they were so afraid that they almost gave up playing. Without [the injured Frank] Lampard and [Gareth] Barry, and with [Wayne] Rooney suspended, they were very restrained," Vieira explained.
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"The turning point was against Sweden when they grew in confidence by winning. They're a physically strong team. They learnt a lot tactically from [Fabio] Capello.
"They have Rooney and especially [Steven] Gerrard. Whoever wants to beat England needs to stop him because he's in great form.
"England have Rooney, [Danny] Welbeck and [Andy] Carroll up front, and are very strong. But if Prandelli says that he plays three or four at the back depending on the type of opponent, it's because he knows his team as well as anyone.
"Traditionally, Italian teams almost always find a way to limit the strengths of their opponents."
England and Italy kick off at 20:45CET on Sunday.