Newcastle boss Rafael Benitez was approached by the Spanish Football Federation about taking temporary charge of Spain at the World Cup, BBC Sport understands.
Cristiano Ronaldo says he is "grateful for the opportunity" given to him by Juventus, as players of his age "usually go to Qatar or China".
The 33-year-old Portugal forward has joined the Italian champions for £99.2m after nine years at Real Madrid.
Liverpool have made an offer to sign c for a reported £62m, a world record fee for a goalkeeper.
Roma are considering the bid but no deal has been agreed and the Italian side are said to want £66m.