On Tuesday, the European Employee Forum of General Motors, the European Metalworkers' Federation, and other European unions called for a prompt decision, fearful that more delays could put Opel and Vauxhall at further risk.
"What we are now witnessing is GM wasting time and money by once more delaying the final decision with an incomprehensible strategy," the groups said in a statement.
GM Europe on Wednesday offered only that it "does not provide any details for GM board of directors meetings," and would not say if or when any word might come on Opel's fate.
Opel spokesman Frank Klaas said only that there would be an announcement "when a decision has been made."
Under the terms of the Magna bid, Magna and Sberbank would get a 55% stake in Opel. GM would hold onto a 35% stake and Opel workers would get 10%.
RHJ sweetened its offer last week, agreeing to provide 300 million euros in cash compared with 275 million euros offered earlier and would expect loan guarantees of 3.2 billion euros from the government, down from 3.8 billion euros.