Schulz made the remarks said during a brief news conference, shortly after the German president announced he would host a meeting next week with Schulz and Chancellor Angela Merkel to find a way out of a political impasse.
Pressure to reverse his anti-Merkel stance had been applied to SPD leader Martin Schulz after the smaller Free Democratic Party (FDP) dropped out of coalition talks earlier in November.
The party, which was a junior partner in Merkel's previous administration, has remained aloof from negotiations between the CDU/CSU, the left-wing Greens and the pro-business Free Democrats following September's federal election.
"The SPD will not be closed to those talks".
"For the FDP, a cooperation with the Greens at the federal level is not conceivable in the foreseeable future", Lindner told Spiegel Online, and ruled out resumption of coalition talks.
Details have not been finalised but Mrs Merkel has always suggested she is open to talking with the Social Democrats, and Mr Schulz said his party would "naturally" accept Mr Steinmeier's invitation.
"The SPD is of the firm conviction that there must be talks", the party's general secretary Hubertus Heil said, emerging from hours of late-night consultations with Schulz.
But he also cautioned that there was "no automatic path" to a solution - which could take the form of a new coalition, or of cooperating as Merkel runs a minority government - and that SPD rank-and-file members would have to approve any decision.
Schulz had said on Monday that, as he interpreted the election outcome as a vote against forming another grand coalition, he was unwilling to enter talks of reviving the deal with the CDU but also said that the SDP was ready to go into a new round of elections.
Two months after an inconclusive election that brought a far-right party into parliament, Merkel is still trying to work out how she can govern and is operating for now in a caretaker capacity.