Referee Stuart Attwell gave the Irishman a straight red after his studs up challenge on Kevin McDonald 80 minutes into the tie - something that means he will miss the second leg tomorrow night.
Attwell spoke to his assistant before issuing the red to the Reading captain, but he has taken to Twitter to defend his actions, insisting he was tugged back seconds before making the challenge.
He said on Twitter: "Great performance from everyone yesterday [Saturday] but still hard work to be done.
"I have to take my red on the chin but it was a genuine attempt to win a breaking ball.
"I was pulled back which meant I'm leaning back and why my foot has gone high. Keep the faith #urzz"
Both sides are back in action tomorrow (Tuesday night) at 7.45pm in the second leg of the tie.