Jamie Carragher has revealed he was shocked at Arsene Wenger’s surprise selection of Yaya Sanogo over Olivier Giroud – hinting something may have happened behind the scenes. The Arsenal manager opted for the untried 21-year-old for the Gunners’ biggest game of the season – leaving top scorer Giroud on the bench.googletag.cmd.push(function() { googletag.display(“div-gpt-ad-1389116196215-0”); });While Wenger attempted to play down the significance of the decision by telling Sky Sports “Sanogo is playing well, simple as that”, it has left many wondering whether Giroud’s recent off-field antics have resulted in his axing from the team. Former Liverpool defender said it was a very bold decision by the Arsenal boss. “Who knows why the sudden change in a massive game. It’s a massive decision and we’re all shocked by it,” Carragher told Sky Sports. He added: “Who knows what’s happened behind the scenes.”Arsenal lost to Munich on away goals in last season’s last 16 tie and will know they have to produce a top performance to defeat the reigning champions.  Read more Arsenal transfer news.