A 3-2 extra-time defeat to Freiburg, who equalised deep into stoppage-time to force the extra half hour, denied Mainz a place in the semi-finals of the cup and limited their chances of qualifying for Europe via the Bundesliga.
"The defeat hurt; it has certainly left a mark on us," said coach Thomas Tuchel, who devised a novel way to raise his team's spirits by depriving them of a football and giving them table-tennis equipment instead.
"Our love of football is somewhat limited right now," he added. "We need anything but football right now.
"We want to have fun and smile, and I think that can only happen right now when we don't play football."
That will obviously change when they take to the field at the Dusseldorf Arena to face a side who are just six points behind and, with a win, could join Mainz in the scramble for European places.
Furthermore, the game marks Fortuna coach Norbert Meier's 50th game on the bench in the Bundesliga.
"If nobody had told me, I wouldn't have realised," he said at a press conference. "I wouldn't mind it being a few more either.
"The Bundesliga is the best thing there is. It's the best league in the world and is now gaining recognition internationally."
One thing Meier has yet to do since gaining promotion with Fortuna last summer is win a game on a Sunday.
"I don't take any notice of such statistics, but we know we have a challenge on our hands," added Meier at a press conference.
"I won't be needing any flowers, I'd be happier with the points."
Fortuna are without the injured Stefan Reisinger and Ronny Garbuschweski, but Stelios Malezas should have recovered from flu.
Jan Kirchhoff, who has already agreed to join Bayern Munich in the summer, is absent for the visitors, as is Nikita Rukavytsya.