Wenger was well aware of Rooney even before he broke through at Everton as a 16 year-old.
Keown told the Daily Mail: "I saw Nicolas Anelka as a 17-year-old at Arsenal and I'd never seen anything like it. The same with Patrick Vieira, I remember his first pass was pinged and it was like 'Phwoof'.
"It was interesting to hear Arsene Wenger say six or seven years ago that Rooney was the best young English talent he'd seen and that was before Rooney lifted the roof off.
"He has that tigerish nature. You can see the work and you can see the talent. Alongside him at United, Dimitar Berbatov has loads of skill and touch but that languid style of his means that he doesn't satisfy our needs. Rooney leaves us satisfied."