Fabregas was substituted in the 54th minute of Spain’s 3-0 win over Nigeria in Fortaleza on Sunday, while Soldado went off six minutes later.
“Cesc and Soldado were last night submitted for MRI scans,” the RFEF said in a statement.
“In view of the test results, neither player’s presence has been ruled out for the semi-finals, although their participation will depend on the evolution of the said pains.”
Spain and Italy will lock horns at Fortaleza’s Estadio Castelao on Thursday afternoon. Italy have several injury concerns of their own ahead of the game.
Mario Balotelli (thigh) and Ignazio Abate (shoulder) have both been ruled out, while doubts remain over Andrea Pirlo (calf) and Riccardo Montolivo (nausea).
Elsewhere on Sunday, Uruguay secured their place in the semi-finals with an 8-0 drubbing of Tahiti.
* Spain 3-0 Nigeria
* Uruguay 8-0 Tahiti
* Spain vs Italy
* Brazil vs Uruguay