Sunderland boss Roy Keane tried to sign the 32-year-old defender on a three-month deal in August.
He said: “I had been in contact with Keane on the last day of the transfer window.
“He wanted me but only for three months. I didn’t want to go for three months but Celtic chief executive Peter Lawwell didn’t find a way to let me go permanently.
“I didn’t refuse to leave just to be playing reserve-team football.
“I refused to leave because I wanted everything to be clear, not the way Peter Lawwell, or anyone else, wanted.”
