Originally Liverpool were interested in Stoke’s Asmir Begovic, but Stoke want £10m plus for Begovic and Brendan Rodgers has moved on to a cheaper keeper.
Mignolet, who is only 24, had a great season between the sticks at Sunderland, despite the club’s struggle.
Liverpool will now wait to hear back from Sunderland over their offer – and have a back-up plan in case they are turned down.
That is Real Madrid keeper Diego Lopez. With incoming Real boss Carlo Ancelotti expected to restore Casillas to the first team next season, Lopez will be available for the right price. And Rodgers might entice him to Anfield if the Mignolet move falls through.