MOSCOW (AP) -- Russian lender Sberbank warned Friday that a deal to buy Opel with Canada's Magna International Inc. could still fall through as a deadline to move ahead with the deal looms, news reports said.

Asked if the deal could collapse, Sberbank executive Denis Bugrov said that he "did not exclude the possibility," Russian news agencies reported. He was speaking at the bank's annual meeting in Moscow.

Magna and Sberbank are reportedly expected to agree by July 15 whether to push ahead with the deal to buy Opel from U.S. General Motors Corp. after signing a non-binding agreement last month -- which envisages Sberbank taking a 35 percent stake and Magna a 20 percent stake. GM is restructuring under bankruptcy court protection from creditors.

The deal was courted in Russia as a major coup for the country's troubled carmaking industry -- based on signals that Magna would produce Opel cars in Russia.

But negotations have reportedly snagged over what shape the deal will take recently while rival outside bidders could still bid for the company before a preliminary agreement is signed in July.

German Gref, Sberbank's chief executive, said Friday the deal could be signed by September at the earliest.

"The new conditions have to satisfy the bank and the Russian Federation," Gref said, according to RIA-Novosti news agency. "If the conditions suit us, then we can close this deal."

German officials have stressed that the deal for Magna and Sberbank to rescue Opel is preliminary and have said that, until a final agreement is nailed down, other potential suitors could at least theoretically still be in play.

German Economy Minister Karl-Theodor zu Guttenberg was quoted as telling the Tagesspiegel daily Friday that in view of Opel's financial situation "it's urgently necessary to find a sustainable solution in the summer."

"Alongside the Magna consortium, the Chinese automaker BAIC and financial investor Ripplewood among others are still interested," Guttenberg told the Tagesspiegel.