Giroud helped La Paillade to their maiden Ligue 1 victory last term, scoring 21 league goals in 36 appearances for the French side prior to a summer move to north London.
After a slow start to the new campaign, the French striker has scored five goals in his last six appearances for club and country, and Girard believes Montpellier must stop Giroud if they want to win the tie.
“We know Olivier very well,” said Girard ahead at a press conference ahead of the match.
“He is a goalscorer. He is someone who loves to score goals.
“Unfortunately for us, I think he’s rediscovering his best form. He’s starting to score goals. But we’ve also got some tactics which we can employ to try to stop him.”
Girard went on to express his admiration for the 26-year-old and insisted the striker will try his best to prove he is worthy of his position at one of Europe's biggest clubs.
“I think it was a very emotional game for him when he played at the Stade de la Mosson. It was a difficult game for him," he added.
“I think he’s going to try and show he’s not here by accident but we know how good he is. He’s someone we really rate.
“Olivier has progressed a lot over the last two years. He worked very hard for us for two years and he came to Arsenal and we’d almost sculpted him into the player he is today.
“We’re going to try really and stop them from playing. This is someone who made history at the club. We had great times with him.”