Borussia Dortmund have not ruled out making changes to their squad in the winter window after a poor run of form.
Dortmund are all but out of the Champions League and have lost the Bundesliga leadership to rivals Bayern Munich.
They have picked up only one point from their last four league matches and were beaten 3-1 by Bayern to fall to third in the table.
The run has seen concerns voiced about head coach Peter Bosz and his squad, with the defence looking vulnerable and kicker saying there was no "real authority" in midfield.
On Saturday, CEO Hans-Joachim Watzke told Sky: "If we believe that someone would make us better, then it's possible."
And sporting director Michael Zorc said: "We will monitor our development very closely and also what's on the market."
But Zorc added: "We won't debate our personnel at this stage of the Hinrunde. It would only divert from our actual problems."
His comments came after Sport Bild linked Ajax defender Matthijs de Ligt and attacker Kasper Dolberg with a winter transfer to the Westfalenstadion.