Cameron was stretchered off in the second half of the Hurricanes' 52-10 Super Rugby hammering of Moana Pasifika on Friday night, with coach Clark Laidlaw conceding "it didn't look good" for the classy one-Test playmaker.
It came three days after the Hurricanes revealed they will be without current All Blacks utility back Ruben Love for at least a month with an ankle complaint.
Clark has said Love will be his first-choice fly-half this season.
Barrett said losing both players in quick succession was a major blow and he felt disappointment for Cameron, who spent much of last season recuperating from a serious knee injury to his other leg.
"It's a sick feeling when you see a good mate of yours go down, I'm gutted actually," Barrett told journalists on Saturday.
"He's very important to our squad, you saw the difference that he made when he came back at the back end of last year.
"And with Ruben being out, we need our 10s."
Clark said the injury was a "hammer blow" for 29-year-old Cameron, whose lone All Blacks appearance came against Japan in 2018.
"It'll take a wee bit of sinking in. We'll have to get around him if it's serious."
The injury soured an impressive Hurricanes attacking performance, led by a hat-trick of tries to Josh Moorby and a double for fellow-winger Fehi Fineanganofo.
Their eight-try effort came after a first-round bye, while Moana had open
ed their season with a win against Fijian Drua in Lautoka last week.