Milan won 2-0 on the night.
Abbiati said: "I am not worried, as the attitude is the right one. We might have made a few mistakes, but we attacked and had several chances. When we lost the ball, we'd fight to get it back straight away, so this is the right approach.
"We played well and it wasn't easy, as Celtic move very well in attack. We defended strongly and didn't allow many scoring opportunities, knowing that sooner or later we would score. It was very important to get the three points tonight."
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