Manchester United blocked Jose Mourinho from making a managerial return to Porto in January 2016, according to the Portuguese club's president Pinto da Costa.
Mourinho won the Champions League with the Primeira Liga giants in 2004, before going on to manage Chelsea, Real Madrid, Inter Milan, United and current side Tottenham Hotspur.
Porto approached the 57-year-old to take over on a short-term basis four years ago, shortly after his second spell at Chelsea had come to an end, but he had already allegedly verbally agreed to take over from Louis van Gaal at Old Trafford.
Da Costa explained to FC Porto em casa: "We were without a coach in the middle of the season. I approached Mourinho, who had a contract with Manchester United but he was only going to start the following season, and asked if he could come until the end of the season before his move to Manchester.
"It seemed impossible. But not for him, he said yes. There was a cup final at the time, a League Cup final and he said he was coming.
"And when we were thinking it was possible, Manchester United did not authorise it as they argued that we could be opponents in a European competition.
"But a lot of people ignore the fact that, without any conditions, Mourinho was available to spend half a season at Porto in an emergency. It is a fact that is unknown, but it shows the affection with which he was."
Mourinho lasted less than three years at United and has since returned to management with fellow Premier League side Tottenham.
