However, Germany, which along with France is seen as the driving force behind the European Union, has been unable to give a clear response to his suggestions for a post-Brexit Europe as Merkel struggles to form a government.
Speaking on behalf of Merkel's CDU, her Bavarian allies CSU as well as the SPD after the first day of talks, the Centre-left SPD's Lars Klingbeil said: "The three party leaders made it clear in their opening statements that given the election results, we can't just go on as before".
The SPD had initially pledged to go into opposition after picking up a historically low 20.5-percent share of the vote in September.
But Zdzisław Krasnodębski, a member of the European Parliament from Poland's ruling conservative Law and Justice (PiS) party, said Schulz's comments showed his "aspirations to dictate how other countries should behave".
"We are not drawing red lines, but we want to implement as many red policies as possible in Germany", he said, referring to the party's color.
Debra Messing Calls Out E! - While Being Interviewed on E!
Sadler, who had been with E! for more than a decade, announced on her personal blog last month that she left her position after recently learning that her male co-host's salary was almost double her own. "We people to start having this conversation that women are just as valuable as men".
The SPD reluctantly agreed to exploratory talks and is playing hard-to-get. The SPD leadership is due to recommend on Friday whether or not to start those talks, and it will then be up to an SPD party congress on January 21 to make a decision.
A coalition between Merkel's CDU/CSU alliance - which lost ground to the AfD in September's ballot - and the SPD has run Europe's largest economy for eight of the past 12 years.
Volker Bouffier, a senior member of Merkel's Christian Democrats (CDU), told Rheinische Post newspaper his party meant to form a grand coalition but that it could not come at any price, while Bavarian CSU leader Horst Seehofer said participants needed to come to an agreement.
Those negotiations, if they happen, would likely take weeks and the Social Democrats have promised to hold a ballot of their entire membership on any coalition deal that emerges.
Some see this as Merkel's last chance to form a stable government after talks with the Free Democratic Party and Germany's Green Party failed in November.