Koscielny predicts 6ft 4in Giroud, a £13m buy from French champions Montpellier, is set to be a Premier League hit.
"I played with him at Tours and he was a great player then. Now he is even more confident and scores a lot of goals.
"I know his qualities and he will give a lot for us. I know he has the physical quality to play in this league. For a striker it is about confidence and I am sure he is working hard to start well with Arsenal.
"He is tall, like Marouane Chamakh, and is also good with his back to goal. I think he will be happy here."