• First-choice Liverpool goalkeeper out until mid-October • Klopp says Duncan had ‘different idea’ of when he should play

Liverpool will be without Alisson for at least another month, as their first-choice goalkeeper works to ensure there is no recurrence of his calf injury later in the season.

Alisson has been sidelined since the opening game of the campaign against Norwich, when he damaged a calf muscle while taking a goal kick, and Liverpool have been reluctant to put a precise time-frame on his recovery. That remains the case although the manager Jürgen Klopp has admitted he does not expect the Brazil international to return until after the next international break in mid-October.

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Liverpool have an intensive workload of seven matches before the October internationals including Premier League games against Newcastle, Chelsea, Sheffield United and Leicester plus Champions League fixtures with Napoli and Red Bull Salzburg. Alisson’s target for a comeback will be the visit to Manchester United on 20 October but Klopp will not take any risks with the fitness of the £65m keeper.

“He’s improving but we cannot put any pressure on it,” the Liverpool manager said. “It was a really serious injury in the calf and it’s now much better. That’s good for us and good for him but we don’t know [when] exactly. The target was always after the next international break he could be ready but we don’t know. Hopefully everything will be fine for the rest of the season. That is the plan.”

Summer signing Adrián has deputised well in Alisson’s absence with his penalty save from Tammy Abraham decisive in the Uefa Super Cup final defeat of Chelsea.

Liverpool’s demanding schedule could see them play twice a week until January, and Klopp has told Joe Gomez and others who have not featured regularly they will be invaluable over the coming months.

Klopp, who expects Naby Keïta to return to training next week following a hip injury, added: “I have said that to them already. They know it. The time coming up is the most intense period, right through until January. It is a slog, absolutely.”

The Liverpool manager, meanwhile, has claimed impatience was a major factor in Bobby Duncan’s falling-out with the club and move to Fiorentina. Duncan was sold for £1.8m this month after his agent, Saif Rubie, issued an extraordinary statement accusing Liverpool of mentally bullying the striker.

But Klopp said: “We wanted to show him the perspective here but that is a message you deliver and if nobody gets the message then you cannot change that. Obviously he had a completely different idea and especially about the timescale of how quick it has to be. We had to accept that.”