Borussia Dortmund CEO Hans-Joachim Watzke said he will clean out the entire team at the end of the season if results don't improve.
Michy Batshuayi, signed on the last day of the transfer market from Chelsea, scored twice on his debut last Friday, helping Dortmund to a 3-2 win against Bundesliga bottom side Cologne.
However, the result couldn't disguise another poor team performance after drawing their three previous games.
Dortmund are currently fourth in the Bundesliga, 19 points behind league leaders Bayern Munich, and Watzke says there could be a fire sale at the end of the season.
"We need a squad adjustment in the summer, things will be clearer after the second half of the season," he told German newspaper FAZ.
"Michael Zorc [Dortmund's general manager] has the lead on this, he knows my opinion and expectation."
Borussia boss Peter Stoger took over last December after his predecessor Peter Bosz managed eight league games without a win.
The German club finished third in their Champions League group behind Tottenham and Real Madrid, dropping down to the Europa League knockout stages, where they will face in-form Italian club Atalanta in the round of 32.
Recent team performances have angered Watzke, who said: "The team that won the 2011 and 2012 [Bundesliga] titles, weren't as good as today's team, but had the best mentality imaginable."
A lot of Dortmund's most significant players, such as Nuri Sahin, Sokratis Papastathopoulos and Roman Burki, have failed to produce consistent performances so far.
However, England youngster Jadon Sancho, currently out with an ankle injury, Sweden striker Alexander Isak and Germany winger Maximilian Philipp have all impressed, giving a glimpse of hope for Dortmund's future.