It's not good news for us and hopefully it's not worse
Sharks flanks Jacques Botes and Jean Deysel have both been ruled out for up to four weeks, but Keegan Daniel may return to face the Brumbies this weekend.
Springbok Deysel was replaced early in their Super Rugby match against the Southern Kings after suffering a ligament injury to his ankle, while Botes, who had come on to replace him, has a suspected cracked wrist.
"It's not good news for us and hopefully it's not worse," Plumtree said.
"He'll [Deysel] have another scan tomorrow to determine that."
With Willem Alberts also currently sidelined through injury the Sharks could see their loose forward depth seriously tested in the next few weeks.
However, the Sharks boss did confirm that captain Keegan Daniel is fit again after his knee injury and could feature against the top-of-the-table Brumbies in Durban on Saturday.
"Keegan trained really hard with us this morning and hopefully he'll be able to return this week, which will ease a little bit of the pain," he added.