The 52-year-old Mourinho, who parted company with Premier League champions Chelsea last month, called Rebelo de Sousa a “charismatic winner” in the video message.
“It’s the first time I publicly state my support for a candidate, because I think Portugal needs to make the right choice, more than ever,” said Mourinho, who looked relaxed and was casually dressed, comfortably sitting on a couch as he addressed viewers.
“I have a clear understanding that we need a winner, but not only a winner. We need charisma, and uniting these winning qualities and charisma, I think that’s what Portugal needs right now.
“I know the man and the politician. We need a charismatic winner,” added the former Real Madrid and Inter Milan coach.
“So, without any reservation, I take this public position for the first time: I vote Marcelo and I do so because I am convinced he is the right choice for us.”
Rebelo de Sousa, a 67-year-old professor of law and veteran TV political commentator, is leading the polls in the race to succeed conservative president Aníbal Cavaco Silva with voting getting underway.
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