The former Hoops hitman, speaking exclusively to Football Insider, claims recent criticism aimed at the pair is unfair.
The duo have made 27 appearances between them this season and have often started alongside each other.
Celtic’s defence has often been criticised this season, especially after conceding eight goals in their first two Europa League group games.
However, McAvennie has no problem with the defenders and claimed Ange Postecoglou’s system is letting them down.
“I have no problem with Starfelt and Carter-Vickers,” McAvennie told Football Insider correspondent Ben Wild.
“I think they have had a lot of unfair stick. The real problem is the new system.
“The full-backs go flying up the pitch to join in the attacks. So when there is a counter, those two are left exposed.
“Personally, I think those lads are getting better every week. I just think an adjustment of the system is needed.
“The defence is still the problem, I don’t know how many times I can say that.
“So there is work to do in January but with Jullien coming back, we might just be sorted at centre-half.”
Christoffer Jullien hasn’t kicked a ball this season after picking up a long-term injury during last year’s campaign.
The defender was a regular starter before he picked up his most recent knock.