"It is crucial to get him signed and I am sure that will happen," Rooney told the club's official website.
"Carlos loves playing here, he's enjoying it so I don't see why it will be a problem.
"We saw him at West Ham what a great player he was and how hard he works for the team," he added.
"I had no doubts that we could play together and from training with him when he first came you could immediately see the qualities he had. I couldn't wait to play with him.
"Towards the end of the season we didn't play together a lot, but when we did, we did really well.
"He's been brilliant. He's a battler, he works so hard and has scored 19 goals, which is brilliant."