Schweinsteiger joined MLS club Chicago Fire last week having made just four appearances for United all season.
The former Germany captain and World Cup winner failed to make a single Premier League appearance this campaign, while he was named on the bench just four times.
And having been made to train alone or with the Under-23 side on occasion, Mourinho admits he has regrets over how he dealt with the midfielder.
“I feel sorry for the first period with him, he knows that, I am happy that he knows, because I told him. I will miss a good guy, a good professional, a very good influence in training,” Mourinho told reporters on Friday.
“So I could not stop him to go, even though I know we have so many matches and probably would need him for a few matches or a few periods. But I had to let him go and now publicly wish him and his wife a very happy life in Chicago.
“He’s in the category of players that I feel sorry for something I did to him. I don’t want to speak about him as a player, as a player I would or would not buy. I want to speak about him as a professional, as a human being.
Read the full article on eurosport.co.uk: Mourinho 'sorry' for Schweinsteiger treatment at Man Utd