FRANKFURT, Germany (AP) — Borussia Dortmund's best start to the Bundesliga is all but forgotten amid the turmoil of failing to win in the league since September and its suspension on Thursday of top scorer Pierre-Emerick Aubameyang.

Aubameyang was dropped from the squad for the trip to Stuttgart on Friday for what it said were "disciplinary reasons," without giving further details.

The Gabon forward's suspension adds to the sense of strife at Dortmund, which slumped to three defeats in four games without a win having previously led the league.

The club had been hoping that another start after the international break would bring a badly needed change of fortune to stay on new leader Bayern Munich's tail and maintain its championship challenge.

"You're against the wind when you don't win," Dortmund coach Peter Bosz said before Aubameyang's suspension was made known. "But it's a challenge for me to turn it around. We'll find our way back up again."

Dortmund was five points ahead of Bayern last month. Now six points behind Bayern, in third place.

The tables turned when Dortmund lost its 41-game unbeaten run at home to Leipzig, and Bayern appointed Jupp Heynckes for his fourth stint as coach. With the exception of a German Cup rout of Magdeburg, Dortmund hasn't won any games since. Meanwhile, Heynckes has led Bayern on a seven-game winning streak across all competitions, including the 3-1 win in Dortmund in the last round before the break.

"Not only the results, but also the way of playing displeased me," Bosz said. He took over from Thomas Tuchel in the offseason and has had to incorporate seven new arrivals into the team: Andrey Yarmolenko, Maximilian Philipp, Omer Toprak, Mahmoud Dahoud, Jadon Sancho, Jeremy Toljan and Dan-Axel Zagadou.

Bosz had a brilliant start to the league with six wins and a draw from seven games with a goal difference of plus 19. Dortmund's players thrived on the former Ajax coach's swashbuckling style of football.

But the team's defensive frailties were there to see long before it started losing - first to Tottenham in the Champions League, where Real Madrid added another defeat.

The side nevertheless kept winning in the Bundesliga and avoided conceding until the sixth round, where Lars Stindl scored Borussia Moenchengladbach's consolation of sorts in a 6-1 rout.

Leipzig burst the bubble with a 3-2 defeat of Dortmund on Oct. 14 in a game that either side could have won. The aura of confidence was gone and Dortmund never recovered.

The international break came at the right time for the club, offering coach and players some respite and a chance to look at what's been going wrong. Top players like Christian Pulisic, Shinji Kagawa, and Aubameyang stayed with the team instead of departing for international duty.

"We could train in this break with 12 or 13 first-team players instead of the usual four or five. That's why I'm feeling optimistic," Bosz said.

Friday's game in Stuttgart starts a busy week with Tottenham visiting in the Champions League on Tuesday, then bitter rival Schalke for the Ruhr derby the following weekend.

Now suspended, Aubameyang failed to score in any of his last five games. He hardly featured against Bayern — which hosts Augsburg on Saturday — while his lackluster performances in two games against APOEL in the Champions League also brought criticism.

"Auba has scored quite a lot, unfortunately just in training," '' Bosz joked this week.

The Dutch coach is boosted by the return to fitness of Germany forward Andre Schuerrle, while Raphael Guerreiro and Marco Reus are still working on their comebacks.

Stuttgart, promoted as second division champion last season, has conceded only one goal in five home games on its return to the Bundesliga. The side won four of those games and drew the other.

"Stuttgart is very well organized defensively and doesn't allow many chances," Bosz said. "It won't be an easy task. We'll only be successful if we perform as a real team and enforce our style of play 100 percent."

Another setback would call Bosz's position into question.