Miller saw red following a rash tackle on O'Brien and, after the Motherwell player reacted angrily, both sets of players became involved in a hostile exchange, with O'Brien himself eventually booked.
But in a statement on the club's website, Mancini -- who the photographs suggest was the aggressor, repeatedly tugging the player's clothes -- downplayed the exchange, which was sparked by Balotelli's hostile challenge on Scott Sinclair.