Carlo Ancelotti was worried about Celtic’s recent demolition of rivals Rangers.
The Italian manager will want to defend their Champions League trophy and had a bright start to the campaign with a 3-0 win over Celtic.
Real Madrid initially seemed to struggle in the first-half with Callum McGregor hitting the woodwork.
Goals for Vinicius Junior, Luka Modric and Eden Hazard sealed the game in the second half.
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Ancelotti told BT Sport: “It was like two games, first half we suffered a bit with intensity, second half we had control.
“We were not surprised [with Celtic’s start]. We knew they could start really fast. We were lucky because they hit the post.
“Second half was much better. When we opened to scoring it was easier for us to control the ball.
“We need to improve the speed in the final third and we had a good combination and scored three fantastic goals.”