Grenoble boss Mehmed Bazdarevic - who was hired while Giroud was on loan at another French club, Istres - transfer-listed him and declared that Giroud, "did not have the level to play among the elite".
But as Arsenal prepare to seek revenge for Dortmund's 2-1 win at the Emirates, Giroud said: "It was a long time ago. I was young, just 19, and I was not mature enough, but I grew up step by step.
"First, in the French second division, I proved I could score a lot of goals and do well. And after I improved myself, I had a lot of thrust and confidence to continue and keep it up.
"I succeeded in doing it at that level and won the championship. Everything I did on the pitch is my answer for people who wanted to blame me.
"Maybe, I tried to do my job on the pitch and score goals and never mind other people. But I believe in my qualities and my game, so I don't care about it.
"There is no doubt that it was a good inspiration for me, though."
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