Glencore's efforts to launch a takeover of Xstrata are looking increasingly uncertain, with the company missing the deadline to raise its £18 billion offer.
Earlier this year the two companies confirmed they were in talks to form a monster $US82bn new entity that would rival the likes of BHP Billiton.
But the deal has been opposed by a number of shareholders and advisors, with concerns over the "wholly excessive" payments Xstrata executives would receive if the deal proceeds.
The Guardian reports advisory service Pirc has also expressed concern about due diligence and independent representation.
"There is no evidence that Xstrata has undertaken appropriate due diligence on Glencore in order to protect Xstrata shareholders," Pirc said.
"In addition, the level of independent representation on the board is insufficient … shareholders are not provided with adequate assurance that the proposed transaction has been subject to an appropriate level of objective scrutiny."
The Guardian reports that while the Glencore/Xstrata merger "is not quite dead" the current roadblocks mean the deal is unlikely to go ahead.