The police said the inspection of the boat «forms part of a routine check of boats that is carried out each summer».
It added that the inspection aimed the boat’s owner, not Ronaldo as its renter.
The authority’s aim was to determine if the boat’s holder, «in this case a charter company», is correctly applying a tax exemption for crafts that are available for rent, but is not applicable once they are rented.
The plot outline was first reported by Spanish magazine HOLA on Wednesday. HOLA published what it petitioned were photos of agents boarding a yacht supposedly rented by Ronaldo in waters immediate the Balearic island of Formentera.
The boat inspection is not related to an investigation into Ronaldo’s relationships for alleged tax fraud.
The Real Madrid player is set to be questioned by a judge on July 31 after a splendour prosecutor accused him of four counts of tax fraud totalling 14.7 million euros (£13 million).
Ronaldo has denied any wrongdoing.