The Video Assistant Referee [VAR] was once again in the firing line after another controversial night in the Champions League.
UEFA brought forward the use of the technology for the last-16 stage of this season's competition , and the controversial system has caused more consternation.
In the first round of fixtures, Ajax were furious after their opening goal against Real Madrid were ruled out for a controversial offside call .
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Now the referee for Manchester City's first leg trip to Schalke, Carlos Del Cerro Grande, was at the centre of the confusion after a penalty was awarded to the home team in the first half.