Warburton’s assistant David Weir was sent from the dugout for abusing the fourth official.
Rangers also had defender Philippe Senderos sent off, after he picked up a second booking for a needless handball.
Speaking to Sky Sports, Warburton said the result was “hugely disappointing”.
He said his players were guilty of “poor decisions” and said the handball by Senderos “hurt us”.
Asked what led to Weir being sent to the stands, Warburton says his assistant was “hugely frustrated that Barrie McKay was taken out on the touchline by a player on a yellow card”.
“At 3-1 down, it was already an uphill task, but that could have made it 10 against 10,” he said.
However, it is thought that the player who impeded McKay was Mikael Lustig, who wasn’t on a yellow card.