The veteran midfielder is set to leave Liverpool at the end of the season when his contract expires.
The 37-year-old joined Liverpool on a free transfer from Manchester City in 2015 and played a big part in them winning the Premier League, the Champions League, the FA Cup and the EFL Cup.
Despite his age, he has continued to remain a key part of the squad and has made 30 Premier League appearances this season as well.
Alexander-Arnold believes his technical ability on the ball often gets overlooked due to his willingness to work his socks off for the team.
He insisted that he is unlikely to get another team-mate like Milner and feels a number of players have to step up next season to fill the leadership void that will be created when he leaves in the summer.
The Liverpool star told The Athletic: “He’s a criminally underrated player.
“Some think of him as just a workhorse who will do his job. But, technically, James Milner is among the best I’ve ever played with.
“Then there’s everything else he brings to the squad with his leadership. He’s truly relentless in everything he does.
“I’ll definitely never play with anyone like him again. That’s probably the biggest compliment I can give him.
“We will all need to fill that big gap. I don’t think it’s just down to a single person.
“All of us need to step up and ensure that we maintain the standards that Millie has set for the past eight years here.”
Milner has made more than 300 appearances for Liverpool since joining the club eight years ago.
