Tony Docherty has been sent to the stands for what is believed to be "unacceptable behaviour".
Tempers flared just before half-time in the William Hill Scottish Cup semi-final after Aberdeen went down to 10 men on the park following Dom Ball’s red card.
The Dons right back received a second booking for careering into Ryan Christie.
The Celtic midfielder had to be rushed to hospital after appearing to have been knocked unconscious from an accidental collision with Ball.
It’s unclear what angered Aberdeen assistant manager Docherty but it’s believed he was sent off for "unacceptable behaviour" as both sets of players came off the pitch at half-time.
Celtic were leading through a James Forrest rocket that bulged Joe Lewis’ net deep into first-half injury time.
After the restart, Aberdeen were another two goals down – and another man.
Lewis Ferguson was sent off after a shocking challenge on Tom Rogic.
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