Juan de la Cerda y Silva, 4th Duke of Medinaceli (c. 1514 – 1575), Grandee of Spain, was a Spanish nobleman.
During that time he besieged with a fleet the North-African harbor of Tripoli, now in Libya, dealing with Dragut, an Ottoman privateer and admiral.
The force, including ships from Spain, Genoa, Tuscany, the Knights of Malta and the Papal States, was however nearly destroyed in the Battle of Djerba.
In 1567 he was appointed Viceroy of Navarre supposedly staying there till 1572, but it seems that towards the end of 1570, he became head of the household of Queen Anna of Austria, position he held until his death in 1575.
According to Henry Kamen, Medinaceli reported to the king that "Excessive rigour, the misconduct of some officers and soldiers, and the Tenth Penny, are the cause of all the ills, and not heresy or rebellion."