In a telephone conversation with Merkel late on Wednesday, Obama said he had not been involved in the surprise decision by the GM board which has angered the German government.
"The Chancellor made clear that the German government would urge General Motors to present a new plan as quickly as possible and to repay bridge financing by the end of November," said the spokesman in a statement.
GM's move was a reversal of a previous decision to sell a majority stake in its European Opel unit to a consortium led by Canadian supplier Magna and Russia's Sberbank.
"Chancellor Merkel and President Obama agreed to continue to coordinate on the matter," said the spokesman.
Under the original plan, the German government had offered state aid. About half of Opel's 50,000 staff work in Germany.
(Writing by Madeline Chambers)