The former Schalke boss's current deal only has one year left to run, and he says plans to negotiate a new deal have been repeatedly put back to the point where he is no longer sure whether he is wanted.
"Clearly my performance is not good enough to earn a new contract," he said. "But I see that as a source of motivation."
Slomka has led the Reds into the Europa League two years running, taking them to the quarter-finals last term - the club's best achievement in Europe - before guiding them to a seventh-place finish in the Bundesliga.
"We have tried to hold talks numerous times, but always without success," he is quoted as saying in the Hannoversche Allgemeine newspaper.
"Last winter, we were told that we would talk after our training camp in Portugal. Then it was put back to March.
"Then, as my agent asked for an update, (president Martin) Kind told him the talks would be scheduled for the summer.
"Now, they are due to take place in the autumn."
Slomka took charge of Hannover soon after the death of goalkeeper Robert Enke in November 2009 and a string of defeats which saw them plummet towards relegation in 2010.
He managed to save them from the drop and lead them to a fourth-place finish in his first full season in charge, following that up with seventh last year and making him the club's most successful coach.