The former Arsenal man has noted the similarities between the two nations and that of Real Madrid and Barcelona, and concedes that the game on Wednesday will be just as tough.
The Seleccao will look to hit Vicente del Bosque's side on the counterattack, utilising the talents of Nani and Cristiano Ronaldo, while La Roja are bolstered by a Barca spine containing Gerard Pique, Xavi Hernandez, Andres Iniesta and, of course, Fabregas.
"You can liken and compare [the semi-final] to Real Madrid versus Barcelona in terms of the respective styles of the teams," the 25-year-old told English newspaper The Sun.
"Portugal are one of the strongest teams. They defend well and are lethal on the counter. They're similar to Real Madrid and we must be at the top of our game.
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"But there are different players and we also have players from many teams so it'll not be the same."
He went on to discuss his side's muted celebrations after the quarter-final victory over France on Saturday.
"I thought at the end of the game, we were like 'okay we won'," he continued.
"Four years ago, when we won in the quarter-finals, [defeating Italy on penalties] we were all together jumping up and down in the middle of the pitch celebrating.
"We were saluting the fans and our families, we felt the joy of a brutal success when we beat Italy. And now it seems like it was an obligation, something normal.
"But these are the wins that we have to evaluate the most inside us because they are so tough. We've won a Euro and a World Cup and now we're already back in the semi-finals. It's enormous."
Spain will face up against Portugal in Donetsk on Wednesday, with kick-off scheduled for 20.45 CET.