Terry, who has been out with a knee ligament injury, trained on Wednesday and is ready to return to compensate for the loss of Ricardo Carvalho.
Carvalho limped out of the action in the first half at Reading on Wednesday night with a knee injury, and Mourinho is expecting to lose him for a long period.
He said: "I think I am going to be without Ricardo for a while but John Terry is back.
"I lose one central defender but I win another one. John was back in training today with no limitations. He trained for one-and-a-half hours with the reserves in a very competitive situation.
"He could have played tonight but I wanted to protect him. He is ready for the next game so Steve McClaren can drink some champagne tonight after that information."