The NSW Waratahs have lost Test forward Ned Hanigan for at least month in an injury blow that all but rules the 23-year-old out of Wallabies selection for next month's three-match series with Ireland.
Hanigan had been expected to be sidelined for two weeks after hurting his knee in Saturday's Super Rugby loss to the Crusaders in Christchurch.
But Waratahs coach Daryl Gibson on Wednesday revealed Hanigan might be out for up to six weeks.
"He's probably more on the four (weeks out) side, which is really positive, and we just hope to get him back," Gibson said.
The enforced layoff rules Hanigan out of Saturday night's hosting of the Highlanders, next week's trip to Hamilton to face the Chiefs and the round-16 conference derby with the Queensland Reds in Brisbane.
Super Rugby then breaks for the June Tests, but that will be of little consolation to Hanigan and Wallabies coach Michael Cheika.
Despite playing mostly in the second row this season for the Waratahs, Hanigan played 12 Tests last year as a blindside flanker for Australia.
His injury has opened the door for Tom Staniforth to partner Rob Simmons in the second row for the Highlanders clash at Allianz Stadium.
Ryan McCauley has won a spot on the bench as reserve lock.
Fortunately for Gibson, Simmons has overcome a shoulder injury, while flanker Will Miller and hooker Damien Fitzgerald have both passed head injury assessments after being concussed against the Crusaders.
Gibson continues to rotate his halfbacks, with Jake Gordon to start on Saturday and Nick Phipps promised to return next week against the Chiefs.
In the only other change, Tolu Latu has been named on the bench as reserve hooker in place of Hugh Roach.
Israel Folau, Cam Clark, Curtis Rona, Kurtley Beale, Taqele Naiyaravoro, Bernard Foley, Jake Gordon, Michael Wells, Michael Hooper (capt), Will Miller, Rob Simmons, Tom Staniforth, Sekope Kepu, Damien Fitzpatrick, Tom Robertson.
Res: Tolu Latu, Harry Johnson-Holmes, Shambeckler Vui, Ryan McCauley, Jed Holloway, Nick Phipps, Lalakai Foketi, Bryce Hegarty.