The Italian reacted angrily to having a goal disallowed and being denied a late penalty in the clash with the Dutch champions and confronted officials after the full-time whistle.
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“Why wouldn't the manager of a football club be frustrated?” Platt said to reporters.
“Why wouldn't we all be frustrated? Players are frustrated, supporters are frustrated, staff are frustrated.”
After approaching the referee, Mancini was also shown to break into argument with a cameraman, but Platt has played down the incident and believes there is no need for such media scrutiny.
He continued: "Robbie has gone onto the pitch and spoken to the referee. As he comes back, he turns around and has a camera in front of his face for 30 yards.
"He turns around and says, in English, that basically it is enough now.
"People then want to start talking about what has happened and almost exaggerating the incident."