Australia full-back Billy Slater has been ruled out of next weekend's Rugby League World Cup semi-finals with a knee injury.

The 30-year-old suffered the problem during his side's 62-0 hammering of the USA on Saturday.

He will now miss the Aussies' last-four encounter against either Samoa or Fiji on November 30.

Early reports have suggested that Slater would be forced to sit out the final if Australia make it through.