Negotiations over a new deal for the club's most successful coach have stalled since director of sport
"Everything should be wrapped up come October at the latest."
Slomka has led Hannover into the UEFA Europa League in two consecutive seasons after first saving it from relegation when he arrived in 2010.
His current contract runs until 2013 and he said recently that the breakdown in talks was causing him some consternation.
"Maybe I am not doing a good enough job," he said at the start of pre-season training earlier this month.
Hoffenheim claimed a vital 3-1 win against second-tier Kaiserslautern in the first leg of the Bundesliga play-off.