Australian international defender Patrick Kisnorbo suffered a serious Achilles tendon injury on Monday and would be probably ruled out of playing in the World Cup finals in South Africa this June.

The 28-year-old Leeds United star, who has been outstanding this season after joining on a free transfer, was stretchered off in the seventh minute of his side's League One 2-0 defeat by Millwall.

"He (Kisnorbo) picked up a severe Achilles injury which will rule him out for the rest of the season and probably the World Cup," said Leeds manager Simon Grayson.

"It is a huge blow for Paddy. He's been a real warrior this season."

Kisnorbo, capped 18 times since making his debut in July 2002, had been expected to be named in Pim Verbeek's Socceroos squad for the World Cup finals.