The accident occurred on Tuesday at around 6pm.
A grey BMW car is said to have turned onto a side street in Madrid and crossed the bus lane along which Cifuentes, 49, was legally riding her scooter.
The car driver tested negative for alcohol and drugs.
Ambulance crew found her to be conscious and aware of what was happening but noted that her blood oxygen levels were very low, at which point they decided to fit a breathing tube and move her to Madrid's La Paz hospital.
According to a hospital statement , Cifuentes suffered "serious chest injuries for which she requires artificial breathing apparatus."
Doctors revealed that she had broken five ribs which had punctured her lungs.
Spain's Queen Sofia, President Mariano Rajoy and leader of the Socialist opposition Alfredo Pérez Rubalcaba are among those to have already sent messages of support.