The 40-year-old has opted against remaining with the Swabians and hopes understudies Sven Ulreich and Alexander Stolz will prosper following his departure.
"Staying would be unfair on Sven Ulreich," he told the Bild newspaper. "He will be rivalling Alexander Stolz and they are both looking forward to the challenge."
Asked if he would consider staying on a while longer, particularly since Ulreich has a serious injury and may miss the start of next season, Lehmann said he could "rule that out".
It appears the only scenario in which former Germany international Lehmann would prolong his playing career is if a Premier League club came calling.
He recently claimed that he felt good enough to play another year in the English top flight and an offer to do so may change his mind about retiring.
"I am planning to retire, but you just never know," he added.
"I am still really enjoying playing football."