Magna and its Russian partner Sberbank should know within the next five weeks whether they will complete their takeover of Vauxhall and Opel.
Sources close to the talks have told news agency Reuters that GM and Magna's negotiations should be far enough advanced by 15 July that they can reach a conclusion that serves as the basis for a contract.
Ever since Magna was announced as the preferred bidder, the German and UK governments have stoked suggestions that another company could still out-bid Magna. Many viewed this as political manoeuvring, in a bid to persuade Magna to minimise job losses.
Neither Magna nor GM Europe would comment on the timeplan.
However, GM and Magna are reported to have made significant progress with recent negotiations, which are reported to have included settinga licence fee that Opel and Vauxhall will pay for access to GM technology.
Other sticking points still to be resolved are said to include a designation of where Opel can sell cars, and who will carry the estimated 4 billion Euros (£3.4 billion) of risk in pension debts should Opel file for insolvency.
Rival bidders waiting to see how the talks progress are said to include Fiat and Beijing Automotive Industry Corp.