There was a point this summer in which Liverpool fans were looking to Agger to carry the defence, guiding the Reds' other defenders with his experience and footballing intelligence.
A poor season for Martin Skrtel last year ended with Jamie Carragher's retirement and the recruitment of 32-year-old Kolo Toure on a free transfer from Manchester City.
Liverpool suddenly looked over-reliant on Agger.
Switch to October 2013 and Liverpool's defence now has options in abundance, a mixture of youth and experience, as well as the luxury of experienced youth.
It's a wonderful "selection headache" for Brendan Rodgers, but one that also raises questions about the immediate and long-term future of the Danish international at Liverpool.
John Aldridge makes a good point in his column for the Liverpool Echo this week.
"Because his vice-captain and one of his most influential defenders Daniel Agger is available again and under normal circumstances would expect to step straight back in. He didn’t on Sunday, and I wouldn’t expect him to come back in this weekend either."
With the return of Luis Suarez to form a partnership in attack with Daniel Sturridge up front, Brendan Rodgers is edging in his three at the back idea.
The idea works, in theory, with three central defenders at the back, being helped by a fourth - one of the wingers dynamically switching depending on the phase of play in the game.
With a full strength team available, Rodgers would look to Glen Johnson on the right and either Jose Enrique or Aly Cissokho on the left to be this fourth man.
Against Sunderland on Sunday, the back three of Kolo Toure, Martin Skrtel and Mamadou Sakho could do no wrong. It worked. Fans are saying, why change it?
Agger's going to have a tough time getting back into the starting 11 if Sakho continues playing like this. Impressive.— LiverpoolFC News (@LFCTransferNRS) September 29, 2013
A recent "freak gym accident", per the Independent, forced him out of action for the games away at Swansea and away at Manchester United, before he was substituted after half-time during the Southampton match.
Now Agger returns to a defence in which all three defenders are vying for their place in the team—and doing a consistent job at that.
In Toure, Liverpool have a natural and experienced leader who is looking stronger with every game played in a Reds shirt. He can command the right side of a three-man defence well, but as he showed against Southampton in the league, he's not a natural right-back.
It looked certain in the summer that Skrtel would leave, but since his return against Manchester United in the Premier League last month, he's looked almost back to his best.
Sakho is adjusting fast to the pace of the Premier League and brings with him the experience of playing against physical and strong players in France's Ligue 1.
One of Agger's greatest attributes, however, and something that could give him the edge over Skrtel, is his distribution.
Rodgers may bring Agger back into the side in a sweeper-type role between Toure and Sakho, allowing the Dane to move forward safe in the knowledge that Toure and Sakho are comfortable behind him.
Would like to see Agger replace Skrtel on Saturday, playing between Sakho and Toure as a sweeper, bringing the ball out of defence.— Matt Ladson (@mattladson) October 1, 2013
Needless to say, if Rodgers is to keep his three-at-the-back system, four won't go into three.
The signings of Sakho and Tiago Ilori—both young and very talented first team players of the present and future show Rodgers is thinking ahead with his defensive recruits.
Liverpool conceded 43 goals in the Premier League last season. Cut that down and there may just be a few more points on the board.
Rodgers has identified his side's defensive weaknesses and is running a recruitment policy based upon that. The long-standing issue of conceding from set-pieces has continued this season:
Agger is approaching is 29th birthday, and whilst as a defender of his stature, he still has a long and no doubt successful career ahead of him, Rodgers is doing right in finding his long-term replacement.
23-year-old Sakho is a prime athlete now ready to learn the intelligence he needs to become one of the Premier League's best. Agger has that advice at his disposal, now entering his seventh year in English football.
Whether the long-term future of Agger at Liverpool is something within Rodgers' vision may well depend on this mentoring stage with Sakho, and eventually, 20-year-old Ilori.
The likes of Andre Wisdom and Martin Kelly, potential centre-backs in the making could do well to learn from vice-captain Agger also.
Barcelona expressed their interested in Agger in the summer, and Liverpool may see soon as a good time to cash in, before age depreciates his value quickly.
But the same can be said for 28-year-old Martin Skrtel and 29-year-old Glen Johnson.
If Agger does face a battle to regain, and then retain, his place in the heart of the Reds' defence, whether that be in a back three, or four, the competition can only be good for Liverpool.
Rodgers now has a plethora of defensive options at his disposal. As he continues to adopt the pragmatic approach game-by-game, we will see a Liverpool defence evolve to fit the the team-wide system.
Agger will be part of that evolution in many ways, whether he is part of Rodgers' long term plans or not—as world-class competition for a starting place, a mentor and a leader.