The 23-year-old, who has played 53 games, injured his posterior cruciate ligament on Tuesday at The Falls Music and Arts Festival in Victoria.

 

Clarke will likely miss the club's trail games against West Coast on February 18 and the Western Bulldogs on February 26 and be hard-pressed to face Collingwood in round one.

 

It is the second season in a row that an injury suffered late in the pre-season has jeopardised Clarke's start to a premiership season after a calf injury saw him miss the first seven rounds of 2013.

 

"At this stage Zac is not expected to require surgery and will undergo a normal rehabilitation program for the injury," Fremantle football manager Chris Bond said in a statement on Thursday evening.

 

Clarke played 17 games in 2013, including Fremantle's Grand Final loss to Hawthorn.

 

The Falls Festival was held near Lorne between December 28 and January 1, drawing a crowd of about 16,000 people.