The Saints skipper was forced off during the first half of his side’s 1-0 win over Reading at the weekend and left St Mary’s on crutches.
Though the exact length of time he will face on the sidelines will depend on his reaction to treatment, it is understood to be highly unlikely he will feature in the Christmas and New Year matches.
That is likely to mean missing games against Sunderland, Fulham, Stoke and Arsenal in the Premier League, as well as possibly Chelsea in the FA Cup.
Saints are hopeful that speculation he faces a prolonged spell on the treatment table will prove wrong.
Lallana’s absence will be a major blow for Saints, such has been his fantastic form this season.