Reds boss Jurgen Klopp confirmed the 29-year-old playmaker is likely to be sidelined until the end of September due to a thigh injury.
Lallana sustained the injury during the Audi Cup defeat to Atletico Madrid on Wednesday and will sit out the start of Liverpool's campaign and England's next two World Cup qualifiers.
Klopp told Liverpool's website: "This is certainly not news we would have wanted.
"Unfortunately, the damage is such that it will likely mean Adam is out for a couple of months, not weeks, so I think we can pretty much rule him out of August and September.
"Beyond that we will monitor and wait and see. He is a boy with a world-class attitude to everything professionally and he has always come back in good time from injury setbacks since I have been here, so we will see."
England travel to Malta for a qualifier on September 1 and then host Slovakia three days later as Gareth Southgate's side look to move a step closer to next summer's tournament in Russia.
Lallana will hope to be fully fit for the Three Lions' final two qualifiers, that take place against Slovenia on October 5 and away to Lithuania three days later.
The former Southampton midfielder will miss both legs of Liverpool's Champions League qualifier against Hoffenheim, with two group-stage matches scheduled for September if the Reds reach that far.
Klopp's men face both Arsenal and Manchester City in the early stages of the Premier League season, with the trip to Newcastle on October 1 Lallana's potential return date.