The former Republic of Ireland international was injured in the Jets' FFA Cup quarter-final loss to Adelaide last week.

The A-League club confirmed on Monday scans had revealed the 37-year-old had suffered major ligament and cartilage damage to which required surgery.

The ex-Premier League midfielder underwent the surgery in Sydney on Monday and the Jets say he's set for a significant stint out.

"Estimated return to play timeframes will be established by the club's medical staff in consultation with the surgeon," the club said in a statement.

The news is a huge setback for Ernie Merrick with the Jets investing heavily to lure the veteran ex-Norwich City player to Australia on a free transfer in August.

Newcastle have the bye in the opening round of the A-League and open their season in an F3 derby against Central Coast on Saturday, October 19.