The Manchester United striker struck twice in the 3-1 win.
Souness said: "He's scoring against Championship players tonight so let's not get carried away with him tonight.
"Yes, on the basis of tonight, he was excellent. But is Rooney up there with the greats in the world? No he isn't. You can't say we'll play him all the time - you cannot say we'll never, ever leave him out, because he isn't undroppable."
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