Daizen Maeda's red card in Madrid completely altered how things went for Celtic against Atletico.
The Hoops were affected by the decision in countless negative ways.
They eventually suffered a 6-0 loss, but centre-back Liam Scales thinks the way the opposition bench reacted to the red card and their closeness to the VAR monitor was unfair to Celtic.
Soccer Football - Scottish Premiership - Rangers v Celtic - Ibrox, Glasgow, Scotland, Britain - September 3, 2023 Celtic's Liam Scales in action with Rangers' Cyriel Dessers REUTERS/Russell Cheyne The streetwise side to Atletico's game is certainly something Celtic could learn from.
The Scottish champions need to do better in some situations and not just accept and be content with everything.
Particularly in Europe, having that added edge to your game is crucial.
Scales recognises this, and he and his teammates display more shrewdness and cynicality when they head to Lazio would be hugely intriguing.
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