Rojo signed for United this week from Sporting CP.
Jones wrote on manutd.com: "The biggest event of the week was the arrival of Marcos Rojo, who trained with us for the first time on Thursday.
"I met him in the morning and he trained well. We all wanted to greet him and make ourselves known because his English isn't great at the moment, which is understandable. It's nice that the other lads who speak the same language can help him settle in and make sure he feels at home. He looks a strong lad, though, and is really comfortable on the ball.
"Marcos' arrival has provided a little boost in the camp and we are determined to bounce back from defeat with a win at Sunderland. The season starts now and these three points are massive for us. We are going to make sure we play to the best of our ability. Talking about it is one thing and doing it is another, but we are focused on getting the job done."
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