Fiat made the announcement on the day mediation over its "put option" - through which Fiat has the right to sell its car business to GM - was due to end.
Fiat said in a statement that it had put back the date "to wait for the conclusion of the process of mediation." The company said the put option is "an important instrument for Fiat, and is valid and can be exercised according to the terms agreed."
The option is part of a 2000 contract that says the Italian company can legally compel GM to acquire the 90% it does not already own of Fiat Auto.
The mediation process, in which Fiat chief executive Sergio Marchionne and GM chairman and chief executive Richard Wagoner negotiate between themselves, began on December 16.