Fabregas, who scored two goals in the tournament so far, has likened La Roja's last four encounters with their Iberian rivals, saying the two sides have similar styles to Barcelona and Real Madrid.
"You can liken and compare to Real Madrid versus Barcelona in terms of the respective styles of the teams," the former Arsenal midfielder told The Sun.
Both teams clashed at the 2010 World Cup quarter-finals were Spain narrowly won 1-0 through David Villa's strike. But Fabregas conceded that their semi-final opponents will be as tough as facing Real Madrid.
Paulo Bento's men will be geared up to counter-attack against La Roja. Players like Cristiano Ronaldo, Nani and Raul Mereiles can break with electrifying speed to hinder the 'tika-taka' rhythm of Vicente del Bosque. While Spain have their strengths in midfield with Xavi Hernendez, Andres Iniesta and Sergio Busquets, the Barcelona trio dazzle the opposition with their marvelous passing game.
"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," Fabregas said.
But there are different players and we also have players from many teams so it'll not be the same," he added.
Spain beat France 2-0 to enter the the semi-finals. However, La Roja have only lost once to their Iberian rivals in seven competitive games. Spain captain and goalkeeper Iker Casillas, who can become the only player to grab 100 victories if his team beats Portugal, believes his Real Madrid team-mate Ronaldo, who scored three goals so far, is yet to play to his full potential.
'His (Ronaldo) season at Madrid was incredible in terms of the way he played, the goals and the records,' the 31-year-old, known as 'Saint Iker', told Marca on Monday.
'I don't think that right now he is at his best level,' Casillas said.
Casillas was also wary of the fact that Ronaldo strikes the ball in a unique way. However, the 'Tango' ball used in Euro 2012 is not as extreme as the 'Jabulani' which was used during the World Cup and heavily criticised by both strikers and goalkeepers. "It doesn't quite reach those extremes but if you give it a good whack it always swerves in a deceptive way,' he said.