The Brumbies are fearing they could be without promising No.6 Rob Valetini for the majority of the season after the teenager's Super Rugby debut ended on crutches.
Valetini will undergo scans on his knee to determine the severity of the injury and how long the back-rower will be sidelined for.
A winning Super Rugby start in Japan against the Sunwolves on Saturday turned into a nightmare for the 19-year-old, who played just 20 minutes.
Valetini was in a knee brace after being replaced by Lachlan McCaffrey, sparking fears of medial ligament damage which could see him miss up to 12 weeks.
Growing up in Melbourne, Valetini is in a select group of players, including Kurtley Beale, Quade Cooper and James O'Connor, to have signed a Super Rugby contract while still in high school.
The injury soured the Brumbies' 32-25 win to open their campaign.
They are away at the Queensland Reds on Friday night.
Brumbies co-captain Christian Lealiifano told AAP after the Sunwolves game that the team was shattered about the potentially serious injury to their young teammate.
"We're really devastated because he is a young kid on debut and he's been fantastic in the last couple of years with us, so we really feel for the kid," Lealiifano said.
The 113kg Valetini was tipped to replace Wallabies veteran Scott Fardy at blindside flanker after the 33-year-old's move to Irish club Leinster.
