Klopp handed the managerial reins to Under-23s boss Neil Critchley for the replay, who would field the youngsters.
And while Mills doesn’t have issue with this, he did have a problem with Klopp’s decision to not be their in person.
Mills told talkSPORT:”If you’re the manager of a football club, you don’t suddenly go ‘well actually I can’t come in just for one game’, just to be there, be at the game, and that’s what I didn’t like.
“He didn’t have to take the team, didn’t have to do the tactics, didn’t have to do the training. Fly in, be there, support his young players who are trying to impress him, and then fly back out again. It’s very, very doable.
Mills added: “I had no issue with him playing the kids, I don’t mind that in the slightest because Liverpool have been sensational this season.
“Jurgen Klopp has been amazing, and they deserve the right to pick whatever team they want to pick. They played a weak side against Everton, and managed to get through.
“I don’t have an issue with playing the kids, but the manager should be there to support his own players first and foremost.
“Some of those players might not play in Liverpool’s first team for a long, long time.
“It was their opportunity to impress the manager and he was sat somewhere watching it on a laptop, I don’t quite get that.”