Former Arsenal goalkeeper Jens Lehmann has told Goal.com he believes Petr Cech will bounce back from his unconvincing debut against West Ham.
Cech, who arrived at the Emirates from Chelsea in the summer, missed an attempted punch from a free-kick and was beaten by a low shot from Mauro Zarate as the Hammers clinched a 2-0 win.
But Lehmann, a member of the Arsenal "Invincibles" team of 2003-04, said he felt the 33-year-old would soon hit his stride at his new club and have a "fantastic" season.
Saying the goalkeeper's uncertainties had "surprised" him, he added: "I expected him to be really good from the beginning.
"But sometimes it takes a while to adapt to a new club, particularly when you are coming from a major rival like Chelsea. It takes time.
"On the other hand, Chelsea disappointed him because he couldn't play there last season.
"He has seen the cruelty in football -- you are a hero one year and the next year you are not even playing any more. That could spur him on to play a fantastic season for Arsenal."
Lehmann said he felt Cech would help the Gunners challenge for the Premier League title, explaining: "He's got the experience, he's got most of the ingredients that a fantastic goalkeeper needs and he is among the best ever goalkeepers.
"It depends on him. I think he's still got some great years to perform at this level. He will give confidence to the whole team, but of course he has to perform."
Cech's West Ham counterpart Adrian also backed him earlier this week, saying: "That is the life of a goalkeeper.
"The goalkeeper can leave with a save or a mistake, sometimes you are the hero and sometimes you are the worst keeper.
"But Petr Cech is one of the greatest keepers ever. He is a great goalkeeper and I'm sure he will show his best in the next game."