Arsene Wenger’s side have failed to win in their last two games, both losses coming against Schalke and now take on the French champions who have just the one point in the group stage so far.
Giroud scored his seventh goal for Arsenal during the 5-2 victory against Tottenham at the weekend and understands the importance of getting a result when he comes up against his former team.
“It’s a must-win match for us because Arsenal have to go through to the next phase of the competition,” the Frenchman told The Sun.
“Montpellier have nothing to lose now they are already eliminated but we have to be careful as that’s when some teams are most dangerous.
“They didn’t become champions of France with no talent. We must not take anything for granted when they come to the Emirates.”
Giroud also hinted that Montpellier are struggling to cope with the success they achieved last season, adding fuel to the fire of his return to his former club.
“I’ve spoken to some of the guys at Montpellier and they have been having a difficult season. It was a big surprise to everyone that we were champions of France and maybe it was hard to digest,” he added.
“Last season things seemed to go our way. We were riding a wave and it seems that wave isn’t there anymore.”