"Of course he could still have come on but he was already past his best."
Wenger admits Milan ace Kaka is a worry: "Kaka made the difference last year in this competition, especially against Celtic.
"He's the guy who can dominate a situation and in 10 seconds get to the other side of the pitch and score a goal.
"Because of him we need to be more cautious in the centre than we usually are. He's especially dangerous at counter-attacking."