The Robins boss declared that it was "never a sending-off" and insisted that his team would have won the game with 11 men.
"I'm not pleased. If we had had 11 men then we would have won the game. MK Dons are a very good side but we could have killed the game off in the first half," he told the club's website.
"I know that we passed the ball but its disappointing that we're talking about the sending off rather than the football."
The result sees MK Dons maintain their unbeaten start to the new league campaign.