Australian Test fullback Billy Slater suffered a knee injury in the latest State of Origin game and will be out of action for up to six weeks, his Melbourne club said on Thursday. Scans of Slater\'s left knee revealed a grade-3 posterior cruciate ligament injury, but he will not require surgery. Slater suffered the injury playing for Queensland in the first half of the second Origin game, on Wednesday, which New South Wales won 16-12 to level the series. It is a major blow for Melbourne Storm, who are leading the National Rugby League competition by four points.