The captain featured in the 4-0 win at FA Cup opponents Yeovil Town.
Mourinho said, "It's fantastic to have Michael Carrick back.
"It's really sad when you think, in May, his career is going to end as a player. But it's a fantastic assistant-coach I am going to have, I believe. I want to help him be better and better but it's a pity to lose a player that does everything well on the pitch."