According to a statement issued by the PJ National Directorate, "the facts took place inside public toilets" in Albufeira, in Faro district, where "the victim was taken by means of a fraudulent device".
The suspects allegedly assaulted the victim "with a knife and then later on the skull" with a fire extinguisher, while they tried to rob her.
The man and the woman will be presented for first judicial interrogation for the application of coercive measures.
The arrest was made by the Criminal Investigation Department of the Portimão (Faro) PJ in collaboration with the Damaia and Casal de São Brás police stations, in the municipality of Amadora, Lisbon district.