Giroud, 26, who netted in the 5-2 win over Tottenham on Saturday, has scored seven times since his £13m move from Montpellier.
He said: "It's a must-win match for us because Arsenal have to go through to the next phase of the competition.
"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."