The Reds signed Adrian on a free transfer last year to act as Alisson’s deputy and the Spaniard has made some high profile errors in big games since his arrival.
Adrian was held responsible by many for Liverpool’s exit from the Champions League last season and he was again shaky when the Reds suffered a shock 7-2 defeat at Aston Villa this month.
There has been talk of Liverpool signing another goalkeeper, but Warner believes it is close to impossible for the Reds to sign a goalkeeper of quality as long as Alisson at the club.
He feels the Brazilian is a massive figure at Anfield and no goalkeeper would consider giving up regular football to come to Liverpool and sit on the bench.
Warner told The Athletic: “Sometimes the devil you know is better than one you don’t. Who could Liverpool have realistically signed keeper-wise this summer?
“No one would have expected Alisson to get another bad injury so essentially you would have been trying to sign someone who has been playing regularly and doing really well elsewhere and is willing to give that up to be a squad player.
“It doesn’t happen often.
“The best example I can think of is when Asmir Begovic, an established Premier League keeper, went from Stoke to Chelsea as back-up to Thibaut Courtois.”
Adrian is tipped to be in goal when Liverpool take on Everton in the Merseyside derby at Goodison Park on Saturday.