Manchester City striker Sergio Aguero suffered a similar injury last month as per Mark Ogden in the Telegraph, ruling him out until the end of January, although he is thought to be close to an early return, according to Manuel Pellegrini, quoted by BBC Sport.
The news will come as a major blow for Agger, already under pressure after an absence through a "freak gym accident," as per Brendan Rodgers, quoted by Jack De Menezes in the Independent, earlier in the season caused him to lose his place in the first team.
Liverpool are also set back by the 29-year-old’s imminent time out, having just begun to recapture some of the form that has made him a fans’ favourite at Anfield in his eight years at the club.
However, Rodgers has assembled a squad capable of dealing with such a blow, and the news that Mamadou Sakho should be fit to face Stoke City in the Premier League this Sunday, according to the Liverpool Echo, will come as a major boost.
The young French defender has regularly kept Agger out of the team this season, and has improved since his arrival from Paris Saint-Germain as he adapts to Premier League life.
The 23-year-old wins 79 percent of his tackles, and makes an average of 12 defensive actions per game, according to Squawka, although his positioning has caught him off-guard several times, with Martin Skrtel often left exposed to cover him.
Skrtel, rested against Oldham, will come back into the fray as Liverpool’s consistent first-choice centre-back.
It is difficult to argue against Rodgers’ re-found faith in the Slovakian, who hasn’t missed a league game since August, and whilst many fans still refuse to believe it, Skrtel has been among Liverpool's best performers this season.
According to Squawka, this season in the Premier League Skrtel has a pass accuracy of 92 percent, has made just two defensive errors and wins 68 percent of his aerial duels.
Furthermore, Callum Fox's brilliant analysis of Skrtel's performance against Tottenham last month for Squawka highlights Liverpool's dependence on him this season.
Though there's still no convincing some fans, who slip into sentimentality about Agger with puppy-dog eyes and continue to use Skrtel as a scapegoat for deeper defensive problems at Liverpool.
Each player is yin and yang; it is lazy to tangle their performances against each other.
Liverpool’s recent congested fixture schedule has also given Kolo Toure some playing time, and he will certainly be ready to take his opportunity should it come at the Britannia Stadium this weekend.
Martin Kelly, too, is nearing the end of his rehabilitation programme and beginning to return to full fitness.
Some top-flight game time during Agger’s absence could really help bring his match sharpness back, though it is likely he will be saved for the FA Cup run.
Every game is winnable for Liverpool now and as they enter a league run against Stoke, Aston Villa, Everton and West Brom, before Arsenal visit Anfield on Saturday 8th February, not leaking goals will be key to their success.
Agger’s injury will be covered by a range of options at Rodgers’ disposal, though he may be cautious of a lack of quality in the full-back positions, with both Jose Enrique and Jon Flanagan still out injured and Glen Johnson underperforming.