The west London derby has taken on greater importance with Chelsea slumping to three successive defeats, starting with their loss on penalties against Bayern Munich in the European Super Cup, three weeks ago.
And Mourinho insists Terry is an integral part of his defensive set-up compared to last year where his fitness was repeatedly questioned by Blues interim Rafael Benítez.
“Last year, he wasn’t playing because (Branislav Ivanović) was playing as a central defender. (Terry) wasn’t even selected and he played from the bench. He went from our big captain to having a very bad season last year. This season the picture is completely different.”
Benítez said Terry was in a “vicious” circle after recovering from a knee injury sustained before Christmas.
For the much of the Spaniard’s tenure the club captain featured just once a week, despite a congested fixture list which saw Chelsea play three times every seven days.
But Mourinho pointed to Terry’s game time so far this season to reiterate what role the 32-year-old can expect to play.
“We have three central defenders,” added Mourinho. “Sometimes John (Terry) and Gary (Cahill); David (Luiz) and John but he is the only one out of four matches who has played 360 minutes. He is important for me. “
The former Real Madrid boss went on to describe how Terry was of a different ilk to many top players in that he never complained if he was not selected.
Mourinho is known to be on cordial terms with Chelsea’s old guard, including Frank Lampard, Ashley Cole and, of course, Terry.
“Off the pitch I have a fantastic relationship with him. What makes the real difference is when they play and when they don’t play,” he said, speaking at a news conference.
“John, Ashley Cole and Frank Lampard are the kind of examples where the manager is the manager and he decides what is best for the team.”