Mancienne has impressed McCarthy with his ability to adapt into his position just in front of the back four.
He said: "We knew he wasn't just a big head-it-and-kick-it centre-half. He went and performed that midfield role he's currently in, shoring it up for us at Tottenham to start with.
"But he's just got better and better at it. He's only just started at it but things have developed from how we were at the start of the season.
"We recognised we had to change it and he's found himself a slot there and it will be hard to move him out.
"He's doing it very well for me and he's doing a terrific job."