The former West Ham hitman, speaking exclusively to Football Insider, insisted the stopper will instantly improve the Magpies’ backline.
Dubravka, 32, featured on the bench for the first time this season as Newcastle lost 3-0 to Chelsea on Saturday.
The stopper has missed the start of Newcastle’s last two league campaigns through injury.
Freddie Woodman started the season as the Toon’s number one but was replaced by Karl Darlow after a string of errors.
Newcastle have now conceded 23 goals this season, the most in the Premier League along with Norwich.
Darlow retained his place against Chelsea but McAvennie insists Dubravka’s return will put an end to his side’s awful defensive record.
“He can’t be back in there quick enough,” McAvennie told Football Insider correspondent Ben Wild.
“A strong defence starts with the goalkeeper, once your number one is in, he’s the key.
“You need a settled defence and Newcastle don’t have that. How can you have and stability when it’s always chopping and changing?
“You need your goalkeeper at the back screaming at the defenders. That might be what Newcastle have been lacking.
“I know it’s obvious to say but once you have your number one back in, you will be stronger as a team.
“Their defence is woeful so you would think Newcastle would want to improve it any way they can.”
Newcastle are yet to win in 11 total outings this season.
Graeme Jones remains in charge of the first team following Steve Bruce’s dismissal on 20 October.