With the Gunners having failed to bolster their attacking ranks over the summer, Arsene Wenger finds himself short on goalscorers.
Giroud has helped to shoulder the burden, with a bright start to the season seeing him net eight times.
He has, however, shown signs of fatigue of late - with out-of-favour Nicklas Bendtner his only back-up - and Koscielny acknowledges that the demands of leading the line in every game are starting to take their toll.
The French defender told The Sun: "It's true that he's not scoring but he is setting them up, like he did against Dortmund.
"But he's also playing game after game and hasn't had a rest, so maybe he's feeling a bit of fatigue.
"He's very important for us - strong and always answers the call on the pitch.
"If you look at the games, he weighs enormously on the opposition's defence. All the balls he wins are in the air with his back to goal. He works very hard up front."
Giroud and Arsenal drew a blank in their last outing against Manchester United, but Koscielny is backing Wenger's men to offer a positive response to a 1-0 defeat against fellow Premier League title hopefuls.
He added: "We are still confident. The lessons to learn are that we were too shy in the first half and we weren't able to play our game.
"The second half was better, even if Manchester United let us have the ball.
"But we'd played a lot of games so maybe we dropped off a bit physically. Now we have 10 days off and we will have to get the fire going again at home to Southampton."