grella-584

Australia's Vince Grella injured his knee while practicing this week. ((Rick Rycroft/Associated Press))

Australia midfielder Vince Grella has been ruled out of the team's crucial World Cup match against Ghana on Saturday after injuring his knee at training. 

With midfielder Tim Cahill also missing after being sent off in the opening 4-0 loss to Germany and doubts over forward Harry Kewell's ability to play a major role, Grella's injury is a blow to a team needing to avoid defeat to stay alive in the competition.

Australia plays Ghana at Royal Bafokeng Stadium in Rustenburg. 

Team spokesman Rod Allen said Thursday that Grella strained a medial ligament during training on Wednesday.

Allen said "it was not a big incident, no one noticed until after the session," adding that Grella should recover for the Group D match against Serbia.