Arsenal defender Per Mertesacker says goalkeeper Petr Cech has brought experience and important ideas since joining from rivals Chelsea.
The 33-year-old endured a terrible start to his career at Arsenal after making two mistakes in the 2-0 home defeat against West Ham United.
But Mertesacker says the Czech international will not be affected by his poor display in the Premier League opener against the Hammers.
"Even when we lose a game, he has some great ideas on and off the pitch," Mertesacker told Arsenal's official website.
"He is very important for us and a good addition.
"He is experienced enough to think about what went wrong [against West Ham], you don't have to tell him. My feeling is he comes back even stronger, so there is no doubt he will be a great addition for us.
"There was not just one mistake [against West Ham] - when a goal happens, there are always three of four small mistakes a lot of the time. It was more down to us to analyse what went wrong in general, and there was a lot.
"Last week was a reminder to ourselves to be aware that everywhere in the Premier League there is big competition."