Cech sealed a £10million switch to the Emirates after playing second fiddle to Thibaut Courtois at Stamford Bridge.
The Czech international enjoyed a glittering 11-year spell in west London.
But Lehmann insists Cech must forget his time with the Blues and move on.
"Before you can have it in your heart to win titles again, you have to get rid of the love you had before," Lehmann told The Sun on Sunday.
Before you can have it in your heart to win titles again, you have to get rid of the love you had before
Jens Lehmann
“At Chelsea, for Petr, it was his passion and he showed great commitment. But, as a professional, he must get over it and needs to know Arsenal want him to win things again for them.
“Yet, let me tell you, that is not an easy thing to get over psychologically it can take a few weeks, even a few months.”
Lehmann thinks Cech can rekindle the Invincible mentality to the Gunners squad.
GETTY
Petr Cech achieved legendary status during his time at Chelsea
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He added: "I cannot believe it has been 11 years now since the club won the Premier League.
“We had another two chances to win it when I was still playing there but they then got rid of all the older guys along with that dressing-room experience and winning mentality.
“Yet with someone in there like Petr, with Per Mertesacker now as captain, they can re-establish this winning attitude and mentality.”