Wallabies captain Michael Hooper is expected to miss four weeks with a hamstring injury sustained during Australia's third-test loss to Ireland on Saturday.

New South Wales Waratahs assistant coach Simon Cron confirmed the minimum month-long time frame on Monday, meaning Hooper's only chance of playing again for the Waratahs would be if the Sydney-based side make the Super Rugby playoffs.

Hooper limped off clutching at his left hamstring after 16 minutes of the Wallabies' 20-16 loss.

Cron says "I know our physios are working with the Wallaby physios ... but it's very early, so they'll keep working through it."

New South Wales is on top of the Australian conference on 35 points, one ahead of the Melbourne Rebels, who they play on Friday as the competition returns to action after a month-long break for internationals.

The Waratahs may also be without Israel Folau, who faces a judicial hearing for making contact in the air with Irish captain Peter O'Mahony during Saturday's test.

The Wallabies are idle until the start of the Rugby Championship on Aug. 18 against New Zealand in Sydney.