According to news magazine Der Spiegel, Bafin, which is currently considering the ACS bid, is concerned about potential irregularities surrounding ACS back in Spain.
The deadline for Bafin's consideration of the bid ends Monday, by when ACS must hand in all additional documents to support its bid.
Bafin's latest official statement says only that it is still considering the bid, but Der Spiegel has cited unnamed inside sources saying that the supervisory board is poised to knock it back.
Bafin is apparently concerned about the financing of ACS's offer. ACS is being sued in Spain for allegedly falsifying its balance sheet. On top of this, Aemec, an organization representing Spain's small shareholders, is bringing an action in a Madrid court to declare a capital increase recently finalised by ACS as illegitimate.
Hochtief has spent months attempting to protect itself from ACS, which already owns nearly 30 percent of the company's shares. The company fears that if the takeover is successful, Hochtief could be restructured at the expense of jobs in Germany.