The 31-year-old, who retired from international football following the 2014 World Cup success, claims that the Germans will be comfortable in France despite their not-so-impressive qualifying campaign.
"[Germany's chances are] very promising," Mertesacker told Arsenal Player.
"The team has changed slightly because a few boys retired after the World Cup and it was a difficult qualification in general, but in the end we went through.
"The Euros are a tough tournament and everyone needs to be fit and ready, so there's always doubt. There's always doubt in Germany and there always has been, even when I played.
"It's good when there are doubts because it keeps everyone going, keeps them focused, and Germany just gets going when the tournament is going on. That's why I think we should be very comfortable going there and just performing as we have always done."