The Belgian goalkeeper has made only two appearances for Jurgen Klopp this season, after the summer signing of Alisson Becker from Roma for £65m has forced him to take a seat on the bench in every top flight and European game, bar the season opener.
Milner has praised Mignolets professionalism, revealing how his attitude in training has had a positive impact on the rest of the squad, especially Becker.
Speaking after his sides victory over Cardiff and as quoted by the Liverpool Echo, vice-captain Milner said: “To be successful, you need a good squad. It’s impossible to win or challenge for a Premier League without that, and it’s the same in Europe, the amount of games you play, the injuries and suspensions you will pick up.
"Someone who hasn’t been spoken about much this season, but Simon Mignolet. It’s incredible how he is around the training ground, he has the best attitude I’ve ever seen in my life.
"Every single day, he pushes himself and pushes Ali and the boys to improve. Nobody will ever speak about him in the press because he’s not on the field, but he’s been so important for us this season.
"That’s exactly what you need, great characters. Even if you’re not playing as much as you would like, the characters in the dressing room are still standing up."
Alissons form between the sticks and the performance of the whole back line this season has been the most notable improvement for Klopps men, with the Reds losing only one game in the league so far this term.
On their squad depth and form defensively, Milner added: “Look at the back four, even. Joe [Gomez] was brilliant before he got injured, then Joel [Matip] comes in. Dejan [Lovren] has done well when he’s played.
"There’s competition for places everywhere, and that’s what you need. Quality players throughout, and some who aren’t even travelling sometimes."
Liverpool currently sit two points clear at the top of the table, although Manchester City have a game in hand which comes in the form of a Manchester derby on Wednesday evening.