Arsenal man Mertesacker and Borussia Dortmund's Mats Hummels formed an unsteady central defensive partnership as the Swiss triumphed in Basle last night [Saturday].
But with the European Championship almost a fortnight away, Mertesacker is not panicking and expects Joachim Low's team to come good.
He told Sky Sports News: "Yesterday [Saturday] was very disappointing for us but we're looking forward to the tournament.
"It's in two weeks and we'll be in good shape I think."
Portugal, Denmark and Holland stand in Germany's way in Group B, from which only two teams will advance to the knock-out stage.
Germany were runners-up to Spain at the 2008 European Championship and then reached the 2010 World Cup semi-finals.
"It's the toughest group in the Euros but we have great experience in the last few tournaments," Mertesacker said, "therefore we are very confident and hopefully we can do a good job."