Herrera, who arrives from Athletic Bilbao, revealed how the focus was on ball work.
He said: "Training has been good, similar to at [Athletic] Bilbao in that we train a lot with the ball.
"The coaches want us to have the ball and keep possession which is great for the players.
"Juan [Mata] and David [De Gea] told me United is a big club, maybe the biggest in the world and they said there is a great spirit here.
"I have [already] seen that. I am happy and just want to start playing now.
"I am very happy and really enjoying being at the club and in the city. The first couple of weeks here have been great."
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