Dalot broke through at Porto as a teenager before joining United at the start of last season.
He told O Jogo: "It is a great pride to be a Porto player and to have been part of the club's history, even for a short time.
"I believe that one day I can represent the club again and win many more titles at the club. Until then, I will continue to celebrate the achievements.
"It is a great pride to be with FC Porto and it is fantastic to belong to the history of the club."