Killen scored for the first time in 23 months, when scoring in the win over Hearts on Sunday.
The striker is out of contract at the end of the season.
“It’s not in my nature to give up. Some players might have chucked it under the circumstances I was going through, but not me,” he said in the Daily Record.
“My contract expires at the end of the season, but I won’t be shouting about wanting a new deal.
“I need to earn a new agreement. That means I need game time and goals for Celtic. I’d love to stay because it’s brilliant being at a club this size.”
He added: “You get written off and fans rule you out for the future, but I’m in the background working my way towards making a fresh impression.”
