Wallabies prop Tom Robertson's World Cup chances have been clouded after he suffered a knee injury in training on Thursday.
Robertson hurt his knee during the main session in Buenos Aires and was on crutches as the team travelled to Salta later in the day.
The prop is yet to learn the extent of the damage with no time for scans before the team left for the weekend's Pumas test but Wallabies coach Michael Cheika said it was a 'significant' one.
If the injury turns out to be an ACL tear, Robertson could be out for up to 12 months and his chances of playing at the World Cup, which kicks off in September 2019, would be very slim.
"I'd say he's done a significant knee injury," Cheika said after the session.
"I won't pre-empt scans or anything like that but it's not looking ideal.
"It was a very innocuous event, no contact, nothing, so it looks significant."
With just three days left on their tour, Robertson will stay with the Wallabies until they return to Australia on Sunday but it seems unlikely he will play again in 2018 with the season wrapping up on November 25.
"He'll stay with us now, there's no point sending him home yet," Cheika said.
"He'll stay with us for the trip and then when he gets home, he'll get the scans he needs and I imagine the operation he'll need after that."
Robertson's injury is the latest in a string of injury setbacks for the Wallabies in recent weeks.
Taniela Tupou, Israel Folau and David Pocock have all been late scratchings ahead of various the Rugby Championship Tests and Tatafu Polota-Nau went back to England after a hamstring injury in training ahead of the side's away South Africa Test.
The 24-year-old has been in and out of the Wallabies side this year but was one of the form Australian props in Super Rugby.
The Wallabies take on Argentina in Salta on Saturday October 6 kicking off at 7:45pm local, Sunday 9:45am AEDT, LIVE on FOX SPORTS and via Channel Ten.