Erik ten Hag has credited Casemiro for "raising the limits" at Manchester United since his August arrival from Real Madrid.
Casemiro has forged a fruitful midfield partnership with Christian Eriksen since swapping the Santiago Bernabeu – where he won five Champions League titles – for Old Trafford.
With United just one point adrift of the Premier League's top four ahead of Saturday's trip to Wolves, Ten Hag believes the Brazil international's presence has had a huge impact on his team.
Asked about Madrid's decision to part company with Casemiro, Ten Hag said: "I'm happy they sold him, he's a magnificent player.
"Our analysis was that we needed someone in the [number] six position. We had lot of discussions about it in this room, but we needed the right player.
"We definitely have the right player. We're happy to have him, he is raising the limits for Manchester United."
Another tenacious South American has emerged as a key part of Ten Hag's side after arriving in the last transfer window, with Argentina's Lisandro Martinez making a centre-back spot his own.
Martinez was absent as United beat Nottingham Forest 3-0 on their return to Premier League action after helping Argentina win the World Cup in Qatar, and Ten Hag hopes that achievement will benefit the defender's development.
"It will be a boost, he has confidence in himself, this experience will strengthen him even more," Ten Hag added.
"Argentina played to win, others played to not lose. He also showed that mentality for Manchester United – when it's difficult to stand up, it will help us even more.
"I didn't doubt him, that's why I brought him in. He has high potential. If he works well, he can make huge progress, he has huge space for improvement.
"That experience is so emotional, and now you have to manage it as a player. It's a good challenge, if you survive the challenge you're going to be a better player."
Meanwhile, Ten Hag confirmed winger Jadon Sancho has returned to training, having been left out since a draw against Chelsea in October after being deemed "not in the right status or fitness state" to play.
"The time is not now but he's making progress and we will see when he is ready to return," Ten Hag said. "He's back in Manchester and started individual training."