The former England international agreed a six-month loan deal with the English champions in the summer after sealing a free transfer to newly-formed MLS franchise New York City.
The 36-year-old opted to remain in the Premier League in order to keep up his fitness before joining the American club in 2015.
"It's football," Mourinho said in this afternoon's press conference. "If you'd said that four or five years ago, I would have said it was strange.
"Even a few months ago, when he signed for the New York team, I was not expecting this, but it was his decision. It's life.
"When he left for New York, I thought he was going there, but it's his life, his decision, and he has my respect for that."