Mats Hummels says Borussia Dortmund can no longer achieve their targets this season after suffering a fourth consecutive defeat in the Bundesliga.
Dortmund are now 15th in the table, just one place above the relegation playoff spot, with Jurgen Klopp's men without a domestic victory since beating Freiburg 3-1 on Sept. 13.
Their Bundesliga form is in stark contrast to their performances in the Europe, where three wins out of three have all but ensured they will qualify for the Champions League knockout stages.
An attempt to give the team a psychological boost by wearing their European kits when they hosted Hannover at the Westfalenstadion on Saturday proved fruitless as they lost 1-0, and they have now taken just one point from their last six league outings.
"We are slowly running out of explanations," BVB captain Hummels told reporters. "We were not the inferior side in any match, and in spite of that just lose one match after another. That's beyond explanation.
"I believe that what we have targeted before the season can no longer be achieved."
Hummels had also appeared to put the blame on the goal -- Hannover's first away from home all season -- on keeper Roman Weidenfeller as he said: "The ball was in the air for a long time, and I was very surprised that it hit the back of the net."
That led Germany's biggest tabloid, Bild, to headline its coverage "World champions row" on Sunday, and on Monday spoke of a "Hummels problem" at BVB, describing his comments on his teammate as "evidence that he is not suited to the captaincy."
Local paper Ruhr Nachrichten also called Hummels' statement "a warning signal" that not everything is right in the dressing room, but the centre-back tried to play down his remark. "The way I phrased it was a bit unfortunate," he said.
Dortmund had spent extensively in the summer to rebuild the squad, bringing in Shinji Kagawa, Ciro Immobile, Adrian Ramos and Matthias Ginter for a total of 50 million euros, as they looked to compensate for the recent losses of Mario Gotze and Robert Lewandowski to Bayern Munich.
However, the rebuilding project has yet to pay dividends and, while the media has been patient so far, there are signs that the 2011 and 2012 Bundesliga champions are running out of credit, with broadsheets like Die Welt and, to a lesser extent, the Schwatzgelb fanzine now expressing concern over the direction of the club.