Vieira admits he's been surprised by how good the Ivorian is.
"I did not know he had such a repertoire when I saw him in Barcelona. He was in front of the defence, playing for others. But at City he has such power of acceleration. It is stunning. And I think he can still make the team do more.
"In addition, we get along really well, he makes me laugh.
"At City, we feel we've brought on his game from his time with Barca."