Australia's Kewell injured his left foot during the World Cup victory over Croatia in the first round.

"Harry has had a follow-up opinion and unfortunately requires further surgery on the foot problem he suffered during the World Cup," Liverpool spokesman Ian Cotton said on the club website.

"The second operation will take place this week in Australia and only after that will we have an accurate idea on the length of his rehabilitation period."

Before the World Cup, Kewell sustained a groin injury against West Ham in the FA Cup final last season.