The England midfielder, who missed part of the back end of last season with a hip problem, will be absent for the start of the Reds' Premier League campaign after sustaining this latest blow in Thursday's (AEST) Audi Cup final loss to Atletico Madrid.

He will also miss out on Liverpool's bid to reach the UEFA Champions League group stages, having been drawn to face Hoffenheim in the play-offs on Saturday.

"This is certainly not news we would have wanted," Klopp told the club's official website. "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."

According to Klopp's timescale on Lallana's recovery, he would miss at least six top-flight matches, including against Arsenal and Manchester City. 

Liverpool begins its domestic season at Watford on 12 August, before travelling to Hoffenheim three days later and host the Bundesliga club the next Wednesday.