The reigning European champions edged a step closer towards a successful defence of their continental crown on Saturday as they eased past France at the quarter-final stage.
A date with Iberian neighbours Portugal now awaits in the last four, with both sides improving the deeper they go in the tournament.
Fabregas knows Spain will not have things all their own way against Paulo Bento's side, with it difficult to tell how a game brimming with creative talent will play out.
He said: "Portugal will be very difficult. They have strong individuals, strong players.
"Apart from their good open play, they are very good on the counter-attack, and we'll have to work hard in that game.
"They have (Cristiano) Ronaldo, Nani, Raul Meireles, Joao Moutinho. They have very good players."
While conceding that Portugal will provide a stiff test, Fabregas believes Spain's dominant performance against France suggests that they, and he, are in good shape.
The Barcelona midfielder added: "We played really well in the first half - actually one of the best first halves in the tournament.
"I played a bit better, but we were playing against France, who played very well. We are very happy now.
"I tried hard, and I ran a lot. I feel good. No matter what happens, the most important thing is that Spain won."
Real Madrid defender Sergio Ramos is also pleased with the progress Spain have made so far.
He said: "This Spain team have taken a step forward. We showed what we're about in this victory (over France) and we're in the semi-finals now.
"We have to carry this on all the way to the final. We can't rest on our laurels because every game is a final.
"Portugal have done really well to get to the semi-finals, so it will be difficult."