Milner joined Aston Villa from Newcastle United for a club-record £12million in August.
Carew said: “James has been fantastic for us. He has been one of our best players this last season.
“He is right up there with Gabriel Agbonlahor and Ashley Young when it comes to importance in the team.
“He has definitely proved he is worth the price tag, maybe even more, not only in the games but in the way he trains.
“He has been in the top three in training every day. He never has a bad day. He is always good for us. He gives everything all the time. His commitment is fantastic.”