The former Everton midfielder signed for United in a massive £26.5 million deal.
Round told MUTV: "When a player comes to Manchester United, they have to have the correct mentality to survive here. It's not enough to be good every so often, you have got to be good every minute of every day.
"Ryan Giggs has said it's not enough to be good in training, you've got to be good with every pass. Not every so often but every pass. Marouane will rise to that, he'll love that challenge.
"He's earned and deserved the right to be here. He's progressed every single year as a player, to the stage where the manager, the staff and the board here feel that he deserved the opportunity to play at this level."
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