Giroud fired Montpellier to their first Ligue One title last season with 21 goals before joining Arsenal in a £12 million summer transfer.
He made a slow start to life in the Premier League, but is now in decent form, scoring five in five matches and he will be up against his former team-mates in their Champions League clash at the Emirates.
Girard said: "Olivier worked very hard for us and we almost sculpted him into the player he is today. We made history at the club and had great times.
"Unfortunately for us, he is rediscovering his best form and starting to score goals, but we have tactics to try to stop him.
"We know how good he is, but there are also lots of attacking threats here at Arsenal."
Captain Mapou Yanga-Mbiwa is looking forward to taking on his old team-mate.
The centre-half said: "I know him and he knows me very well. We will see how we get on - and I will work hard."
Montpellier lost at home to Arsenal in their group opener and their hopes of making it out of Group B are now all but over, sitting bottom with just one point.
Girard said: "I have told the team qualification for the knockout stages is over, but we still have a slight hope of qualification for the Europa League.
"We need to look forward now and build for our Ligue 1 campaign. We need to be very solid, to try to get back to our usual form, and up the Ligue 1 table.
"It is a privilege to play in the Champions League, all of the team dreamt of this and fought for it all of last season.
"It has been quite liberating at times, but we just lacked a touch of experience at certain times in the games. We are just trying to find a bit more consistency in our results and a balance in our play."