For the first time in almost 15 years, England have had to go through a qualifying campaign without the services of either Terry or Ferdinand.
The pair formed England's best central-defensive partnership for over five years, but they both called time on their international careers last season.
Ferdinand had not pulled on the Three Lions shirt since 2011 and it is almost a year to the day that Terry played his last match for the national side, but Cahill still thinks England are in a "transition phase" at the back.
"They were two huge players and they retired at similar times so there had to be a transitional period and that's what it is at the minute," the Chelsea defender said.
"We have some quality centre-backs as well, but when two big names, two big top-class centre-halves come out of the set up there is that worry. People are always going to talk about it."
Following Terry's final game against Moldova, who England face this Friday at Wembley, Roy Hodgson set about trying to find a settled centre-back partnership that he hoped would remain a constant throughout the World Cup qualifying campaign.
The England manager struggled to settle on a solid pairing at the start. Cahill, Joleon Lescott, Phil Jones, Chris Smalling, Phil Jagielka and Steven Caulker were all used in a variety of combinations.
Hodgson seems now to have settled on Cahill and Jagielka as his first-choice pairing after starting with the duo in England's last three matches.
Concerns have been raised about the partnership after Kenny Miller out-smarted Cahill at Wembley last month, but the Chelsea centre-back does not think defence is a weak point in the England side.
"It's obvious people are going to say (defence is a weakness) because of the names that have gone out, but people step in," said Cahill, who looks set to win his 17th cap on Friday.
"I don't think (it is a weakness). Ultimately, results will settle that talk.
"When I was first in the set up I was a lot younger so I feel like I have improved and I feel like I can still improve."
Cahill and Jagielka are expected to have a quiet night against minnows Moldova, but the game in Ukraine four days later will be one of the most testing of the pair's international career.
England know defeat in Kiev could see them slip down to third in Group H with just two matches remaining.
Failing to qualify for the World Cup would no doubt be branded a disaster for the country, and it is something that Cahill himself does not want to happen because he had to withdraw from Hodgson's Euro 2012 squad because of a jaw injury.
"This would be the first opportunity for me to play in an international tournament for England," the former Bolton man said.
"It would be a career highlight for me to play in the World Cup so I am really hungry to get there. I am desperate to get there and I hope we can."
Encouraging attacking performances against Scotland and Brazil do not mask the poor displays that scarred the opening stages of England's qualifying campaign.
Two wins would go a long way to proving the doubters wrong and Cahill knows it.
"This is the crunch time. We have to get results," the 27-year-old said.