Bruce also revealed that David Meyler, who is also suffering from a knee injury, could be back in light training in around a month.
Campbell, though, is just starting out on the journey back to fitness.
"He's had his operation and now it's the long road back," Bruce told safc.com.
"But he's over the worst - the op's been done and now he has to get his head around six months of rehab, which is never easy.
"Knowing the type of kid Fraizer is he will give it his best shot. He's got Meyler to keep him company - David's about a month away from joining in and he's been there and done it.
"It's unfortunate that we're carrying two of our bright young players with serious knee injuries, but they're progressing well."