Duffy was influential at both ends of the pitch on his debut for the Bhoys, as Celtic beat Ross County 5-0 away from home in the Scottish Premiership.
The centre-back joined Celtic from Brighton and he scored on his debut when he netted Celtic’s third on the hour mark.
Duffy was also influential in the other box as well and shored up the Celtic backline, adding more resilience to Neil Lennon’s defence.
Bonner believes Ross County’s performance in the first half was not bad, but they gave away soft goals and allowed Celtic to get away from them.
The former goalkeeper identified Duffy as a key addition and insisted that while he has improved Celtic’s defence, his presence in the other box is also going to be key for the Bhoys.
Bonner told BBC Sportsound: “It didn’t feel at one stage that the game would end with such a scoreline.
“In the first half, I thought Ross County did well but gave away silly goals.
“Celtic really upped the tempo in the second half and got their goals.
“The big positive for them is they now have Shane Duffy, who can defend in his own box but then power home a header in the other.”
Celtic are six points behind table-toppers Rangers but they have two games in hand over their Glasgow rivals.