Guus Hiddink has already stated that he will not be managing Chelsea beyond the end of the season, which means the Blues will have to sign a new manager in the summer.
Chelsea have been linked with a move for Atletico Madrid manager Diego Simeone, while Italy national team manager Antonio Conte has also been considered for the managerial role.
Santo guided Valencia to fourth in the Spanish league in his first season in charge. However, the results deteriorated under him in his second season, and he resigned from the job.
He is a close friend (superdeporte says that the pair share a special bond) of super agent Jorge Mendes, and his trip to Stamford Bridge as has sparked rumours of him being considered as the next permanent Chelsea manager.
While Mendes holds a good relationship with Chelsea, it is highly unlikely that Roman Abramovich would want someone like Nuno to take charge of the club next season.