Doubts were cast about Rangers’ spirit after their 4-2 home defeat by MK Dons in the FA Cup.
But Derry, 35, insists Tuesday’s stalemate against the champs shows the Hoops are united.
He said: “When you lose 4-2, you have to reply in the right manner — we showed that against City. We proved a point to a lot of people and showed we are all in this together.
“Slowly but surely we are closing the gap.
“That was a huge point for us. We now have to take that into the Norwich game on Saturday. It is no good taking a point there and then dropping three. We must progress again.”