By Sean Walsh Liverpool manager Jurgen Klopp has revealed goalkeeper Alisson is set for a longer spell on the sidelines as his injury is ‘serious’. Alisson withdrew from the squad to face Brentford on February 17 due to a hamstring problem sustained in training, while he sat out their victory against Burnley the week prior as he was ill. He has now missed the Reds’ last five games, including last week’s Carabao Cup final win against Chelsea at Wembley. Ahead of Saturday’s trip to Nottingham Forest back in Premier League action, Klopp was asked about when Alisson could return, but he had some b…