The 26-year-old was forced off after 55 minutes of the Reds’ New Year’s Day encounter with Leicester at Anfield with what manager Brendan Rodgers called “a tweak in his thigh”.
The news comes as a blow to Rodgers as the England international was starting to produce the kind of performances which led the Reds to pay Southampton a reported £25million for his services in the summer.
Lallana scored a brace as Swansea were seen off 4-1 last Monday and made his sixth consecutive start against Leicester.
The injury will see Lallana miss both legs of the Capital One Cup semi-final against Chelsea, as well as several Premier League matches.
Lallana has scored four goals and registered two assists in 14 Premier League appearances for Liverpool this season.