The Liverpool No.1 sustained the issue in the first half of the 4-1 win over Norwich City on August 9 and was subsequently ruled out for ‘the next few weeks’ by Jürgen Klopp.
Summer signing Adrian has stepped in for Alisson and enjoyed a fairy tale start to his Reds career with the decisive save in the UEFA Super Cup success against Chelsea.
Alisson continues to work on his rehabilitation at Melwood and Achterberg anticipates a clearer idea of his potential return date after the forthcoming international break.
“Ali is good. He’s in every day for treatment and they try to improve things,” the first-team goalkeeping coach told The Athletic.
“He’s able to do some fitness work in the gym without using his leg. It’s difficult, but you have to try to look forward and be positive. You have to try to turn a negative into a positive.
“They haven’t given us a specific time he’ll be out as it’s difficult to say how quickly it will heal. That’s all with the medics. There’s an international break coming up and we’ll have to wait and see how long it takes after that.
“When something like that happens, you look at everything. Had the training load changed? The reality is that we hadn’t done anything differently in the build-up to that game. Ali felt fine. We have a rule with the goalies that if there’s any kind of issue you always have to talk.
“He actually came back in much better shape this summer than last year when we first signed him. It was all positive and that makes what happened so frustrating for everyone.”