Koscielny, 26, reckons the new man's firepower can strengthen the Gunners frontline.
"We played against him pre-season so we've had a fairly recent look at him," said Koscielny.
"He is a very good player with qualities different from those of our other attackers and he has a great left foot. I think he can help us by scoring goals and, hopefully, help us win things.
"I can't see him having any problems here and look forward to welcoming him. It's some more Polish heritage for the squad, too.