A 3-0 loss at home to Hoffenheim yesterday left the Bavarian club 14 points adrift of safety and seven behind the relegation play-off berth.
Considering they have managed to win only two of their 25 games so far this campaign, Hack believes Furth must now realistically focus on playing in the second division again next season.
"When you lose 3-0 at home to the second-bottom team, then you know what that means as a consequence," he said.
"We have got to be realistic. As long there is still theoretically a chance, we will try everything, but one thing is clear - we have never won a single game at home.
"We can do the maths and see the table and we know what it means.
"Quite clearly, from Monday we start to prepare an honourable relegation to the second division."
Hack hopes that facing up to their destiny will relieve some of the pressure and allow them to go down with a certain degree of pride.
"Maybe we will manage to do a few things that we have not been able to do so far, but we know that something decisive may have happened," he told Sky television.
The club's fans finally lost patience with the team, ironically cheering them at 3-0 down, much to the annoyance of defender Mergim Mavraj.
"We did not deserve to be humiliated by our own fans after the performances we have given this whole year," he said.
"We celebrated a lot together last year and if we go back down, then we should at least go down united."
Hoffenheim could still be following them into the 2.Bundesliga, though, with yesterday's victory not getting them out of danger.
Two points still separate them from a relegation play-off while they are nine adrift of automatic survival with nine games to go.
"This was a good performance, but we are still in the relegation zone," said their coach Marco Kurz.
"It is going to remain tight until the very end. Now we must work hard and earn more wins."