He was eventually sent off after a tackle on Dinamo Zagreb's Ivo Pinto in the 40th minute saw him pick up his second yellow card as Arsenal went on to lose 2-1.
Wenger insisted Romanian referee Ovidiu Hategan was harsh in flashing the second yellow card.
"The first yellow card was Giroud's fault because he protested, even if there was no foul against him. After that he should have not protested to the referee," the 65-year-old Wenger told reporters.
"His second yellow card was completely unlucky to touch the guy. I do not understand the referee.
"It was completely accidental. It happened and I think at that moment it was not a second yellow. It has to be a foul on purpose and it was not on purpose. The referee should have given several yellows tonight based on that.
"We were a bit unlucky. We had a lot of the ball and, as well, we had early chances. I believe the first goal is offside and after that, the sending-off is very harsh," he added.
Arsenal forward Theo Walcott was confident the team can put the setback behind them and advance from the group stage.
"We've still got a long Champions League run. We've had setbacks before and we've managed to bounce back from them," the England international said.
"We should be able to come back stronger. The manager will make sure that it's put to bed in the changing room and that it will stay there," he added.
(Reporting by Shravanth Vijayakumar in Bengaluru; editing by Amlan Chakraborty)
Share
