Cech made two costly misjudgements on his Premier League debut for the Gunners as Arsene Wenger’s side lost 2-0 at home to West Ham on Sunday.
Lehmann, who played in goal during the ‘Invincibles’ season in 2004, admits he was shocked by Cech’s performance but believes the 33-year-old will be motivated to prove a point to Chelsea.
"It surprised me because I expected him to be really good from the beginning,” Lehmann told Goal from the United States, where he is taking part in the Bundesliga Legends Tour.
"But sometimes it takes a while to adapt to a new club, particularly when you are coming from a major enemy like Chelsea. It takes time, if he can forget about it at all.
"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."
Cech cost £10m when he arrived earlier this summer and Lehmann remains convinced that the Czech international is the shot-stopper Arsenal need to topple the likes of Chelsea, Manchester United and Manchester City for the first time in 12 years.
"He is the goalkeeper Arsenal need to win the title," Lehmann added. "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 haven’t spoken to him, so I don’t know how he feels physically now, but 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 arrival in north London has prompted Wojciech Szczesny to join Roma on a season-long loan and the Arsenal legend has backed the Pole to return to the Emirates Stadium with a winning mentality.
"Why can’t he come back? I’ve always said that when you’re too young, you shouldn’t play for a big club when they need you to win something," Lehmann continued.
"It’s about mentality. When you commit to a big club which his ambitious to win trophies, you have to commit to that target with no distractions."
