Mr Muller gave no indication of when a deal might be clinched with Saab's future hanging in the balance after GM nominated two 'wind-down supervisors' last week. The strange move came at the same time GM announced it was still considering bids for Saab.
Mr Muller also said that it was "unclear when we will be done", but did not say whether GM had imposed a deadline for a deal to be sealed.
A GM Europe spokesman had earlier said that GM was still in talks about Saab, but did not say whether GM was talking to one or several buyers.
The talks between GM and Spyker, a Dutch maker of luxury sports cars, came after more than 500 Dutch Saab enthusiasts rallied on Sunday in support of the brand.
Mr Muller denied reports of a joint bid for Saab with another bidder, the investment company Genii Capital, whose offer is backed by Formula One boss Bernie Ecclestone.
CarAdvice will keep you updated with any news as it comes to hand.