Having been dumped out of the German Cup last Tuesday by a shock 3-1 home defeat to Hoffenheim, on Saturday Schalke lost 2-1 at fourth-placed Borussia Moenchengladbach, who opened a seven-point gap over fifth-placed Schalke in the Bundesliga.
With the Royal Blues now 17 points behind Bundesliga leaders Bayern Munich and out of the German Cup, a Champions League exit -- albeit with entry to the Europa League if they finish third in Group E -- would end their interest in all three major competitions.
And it could well be Keller's last game in charge having taken over in December last year.
"You need to ask those in charge who make those decisions," Keller replied tersely when asked about his future after Wednesday' match at Gelsenkirchen's Veltins Arena.
"Yes," said Schalke's general manager Horst Heldt when aked if Keller would be in charge for Wednesday's match, but he refused to comment when asked about next Sunday's home Bundeliga game against Freiburg.
Clemens Tönnies, head of Schalke's advisory board, said it is all about results now.
"Now is not the time to address the question about the coach," Tönnies told magazine Sport Bild.
"It's all about winning our next few games."
Schalke are a side badly in need of a confidence boost after suffering their eighth defeat of the season in all competitions at 'Gladbach.
The Royal Blues can justifiably argue they were the victims of some harsh decisions by referee Felix Zwayer at Mönchengladbach.
With the scores level at 1-1, Schalke captain Benedikt Höwedes was sent off for a second yellow card after a shot on goal ricocheted off his upper arm, earning the Germany defender a red card following an earlier yellow.
To make matters worse, striker Max Kruse converted the resulting penalty, on the stroke of half-time, which proved to be Moenchengladbach's winner.
"That was not a penalty, I was turning myself out of the way (of the ball) and it's a pity the game was decided by a goal like that," said Höwedes.
Gladbach coach Lucien Favre agreed with the Schalke defender.
"The red-yellow against Höwedes was, from my perspective, too harsh. Perhaps it's the rules, but it wasn't necessary," said the Swiss coach.
Only a superb save from Borussia goalkeeper Marc-Andre ter Stegen, deep in extra-time, from a Kevin-Prince Boateng header denied Schalke an equalizer as their luck deserted them.
Höwedes admitted Wednesday's game is "all-or-nothing" now with regards to their season.
Basel kept their Champions League hopes alive with last month's upset 1-0 victory against Chelsea, putting them ahead of Schalke in their qualifying group.