Ralston started the first two league games of the season but has largely been a backup to Alistair Johnston in the Celtic squad.
The 24-year-old divides opinion among Celtic fans with some holding the opinion that he is not good enough for the Glasgow giants, but he has just signed a new contract.
However, Duffy believes Ralston is a good fit in the Celtic squad and pointed out that he has been learning from some top right-backs in the Bhoys team over the years.
He feels that the defender has shown enough in some big games for Celtic that he justifies his place in the squad and insists that there is no point in the club spending money on a backup right-back when Ralston is in the squad.
The former defender also believes Brendan Rodgers admires the character the player has shown to come through some tough times at Celtic.
Duffy said on the Go Radio Football Show: “Anthony Ralston is a good fit for Celtic.
“He is set to play second fiddle, he has been out on loan and as we know he had Mikael Lustig, Juranovic and Johnston – he had some top players in front of him.
“He is learning all the time and he seems to be more confident when he is getting on.
“He is 23 so he is not a kid anymore, he has had enough games under his belt, and he has played some big games now and scored some important goals.
“What do you want to do?
“Go and spend a couple of million on a backup player when you have got a boy there who knows the club inside out, came through the tough times, he had to fight his way to be a first-team squad member.
“I think all of those things mean that you are a strong character and Brendan Rodgers is really happy with him and his ability on the pitch.”
Ralston will hope to get more game time over the course of the season and earn Rodgers’ trust.