The 34-year-old said: "At the end of the day it wasn't what I wanted and it wasn't right for the club or me.
"I'll just keep my options open and it's still possible that I'll sign for Grimsby Town. But we'll see what's offered and what happens."
City are thought to be lining up a move for 22-year-old Tottenham Hotspur defender Alton Thelwell instead, while Jason Price and Andy Dawson's transfers are still on.