Wellington - Crusaders captain Richie McCaw has been sidelined for at least five weeks from the Super 14 competition with a knee injury.
McCaw limped from the field during his side's 6-0 loss to the Highlanders on Saturday, the third straight defeat for the defending champions.
A medical examination on Monday revealed a medial ligament strain but Crusaders' coach Todd Blackadder is hopeful his star flank will return for a three-game trip to South Africa, starting with a clash against the Sharks on April 18.
"It's never a good time to lose one of the best players in world rugby but it's a good opportunity for George Whitelock to step up," Blackadder said of his reserve openside flank.
Former All Black hooker Corey Flynn will be out of rugby for about six months after breaking his left arm in the Crusaders' defeat by the Brumbies last month.