The striker feels he is paying the price for demanding a summer move, and cut a forlorn figure when Stefan Savic went on as City's final sub.
A source close to the forward told the People: "Carlos is very disappointed with the way things have turned out.
"He came back to England committed to giving everything for the team, but he has not been given a chance.
"Carlos was not the only high-profile Premier League player to have been involved in a summer dispute with his club.
"Others, like Luka Modric at Spurs, emerged from those problems with their status enhanced, but Carlos finds himself out in the cold. He feels his only option could be to leave the club."