Borussia Dortmund plan to announce the sacking of coach Peter Bosz on Sunday, Sport Bild and other German news outlets reported, after the spiralling club lost at home to Werder Bremen on Saturday.

The result extended the Black and Yellows' winless streak to eight games in the Bundesliga dating to September, in which time they've fallen from first to seventh place while losing 18 points to league leaders Bayern Munich.

Bosz had described Saturday's match against 17th-placed Bremen as a "must-win," and after suffering a 2-1 defeat, he will pay the price with his job, according to Bild.

Bosz, 54, was hired in June after helping Ajax reach the Europa League final and finish second in the Eredivisie.

His tenure with Dortmund started well, winning six and drawing one of his opening seven league games -- putting Dortmund top of the table while Bayern Munich struggled under then-coach Carlo Ancelotti.

But since the start of October, Dortmund have only managed to beat third-tier Magdeburg in the DFB Pokal, while losing five of eight Bundesliga games. In the Champions League, they only managed two draws against Cypriot minnows Apoel.

Bosz admitted after Saturday's defeat that Dortmund had reached a new low with their performance.

"Bremen deservedly won. Especially in the first half, we played very poorly. That was the worst I've seen since my appointment," Bosz said. "Not only from a footballing point of view, we were simply not aggressive enough in the tackles. Bremen's lead was a logical consequence.

"There was only a brief period in the second half when I thought that could nick it. But after conceding the 2-1 off a corner, we had no comeback. I have to bluntly say: We lacked quality."

He also accepted the blame for the team's form, adding: "We did not play the way exercised in training. If one player had the ball, others did not move. Of course, I'm responsible for all that in the end."

Dortmund captain Marcel Schmelzer, who did not mince words in his own opinion on Dortmund's form, said the players should be held accountable rather than the coach.

"It's us players, who shoot the ball out of bounds, who do not defend the goals, who can't defend set pieces," he said. "The coach can't sub himself on and score the goals himself. I'm sorry if I keep repeating myself on a weekly basis but it's us players [who are at fault] and today's game is annoying me so much."

Dortmund will travel to Mainz on Tuesday before facing Hoffenheim on the following weekend.