Australia lock Sam Carter could be out of action for up to three months after injuring his knee while playing Super Rugby for the ACT Brumbies.
The second row is set to miss the rest of the Super Rugby season after suffering a torn medial ligament in the 22-16 win over the Bulls in Canberra.
Carter, 25, hopes to be back in action for Australia's World Cup warm-up match against the US Eagles on 5 September.
The Wallabies begin their World Cup campaign against Fiji on 23 September.
Australia will also face Uruguay, England and Wales in Pool A of the 2015 Rugby World Cup, which takes place in England between 18 September and 31 October.
Carter, who started 11 Tests for Australia last year, required lengthy treatment on the pitch at Canberra Stadium on Friday following a collision with Pretoria Bulls winger Bjorn Basson.
"He'll be touch and go for the last rounds of the Rugby Championship and then he's potentially playing that warm-up game [against the USA Eagles in Chicago] for the World Cup," Brumbies coach Stephen Larkham told the Canberra Times.
"I think there's still enough time there for him."