Warnock was diagnosed with the injury earlier this week and will be out of action for up to eight weeks.
Blues coach Brett Ratten confirmed the injury in The Age newspaper on Thursday morning.
"At this stage it looks like he will be in rehabilitation for the next month or two," he said.
"Robbie is a talented young ruckman who is still developing and remains an integral part of our plans in 2009 and beyond."
Warnock played 21 games for Fremantle before he was traded to Carlton in October.
Standing 206cm tall, Warnock is expected to shoulder much of the ruck load with Cameron Cloke and Matthew Kreuzer.
Warnock was traded along with Fremantle's no. 69 draft pick to Carlton for picks 24, 56 and 72 in the NAB AFL Draft.
