Gray told talkSPORT: "John is not first choice or automatic choice. He has to play in a position where he fits in, if two out of Ivanovic, Cahill or Luiz don't play, as has been the case when John has played in the bit-part games.
"I've looked back at games Terry has played this season, and against Arsenal and Juventus in September - two big games - John Terry played with David Luiz, when Roberto Di Matteo was manager, and he played left-sided centre-back with Luiz on the right, as he always has done.
"They played Manchester United in the FA Cup recently and Terry was sat on the bench. What does that tell you? Look at his recent record, he doesn't play in the big games. Terry is not starting if Chelsea make the final of the FA Cup and Europa League.
"I'll be amazed if John Terry starts against Manchester City. I think he will have Ivanovic back alongside Luiz, and Terry will be sat on the bench. The only way Terry will get into the side is if there is a problem with players being injured. His days of being first choice, under this coach, are over."