The first set of EU sanctions is due to expire in March and will need to be renewed. German officials say Italy, Hungary and Slovakia will be the most difficult countries to keep on board.
"Putin will be trying to peel countries away in the run-up to March," said one diplomat. Another described the battle to keep the EU united on Russia as a "Herculean task."
Against the backdrop of this fragile EU consensus, ratcheting up economic sanctions further is seen as a "no go" in Berlin for now.
Since February, when the pro-Russian president of Ukraine, Viktor Yanukovich, fled Kiev amid violent protests on the Maidan square, Germany has taken the lead in trying to convince Putin to engage with the West.
Merkel has spoken to him by phone three dozen times. Her Foreign Minister Frank-Walter Steinmeier, a member of the Social Democrats (SPD), traditionally a Russia-friendly party, has invested hundreds of hours trying to secure a negotiated solution to the conflict.
Now, German officials say, they have run out of ideas about how they might sway the Russian leader. The channels of communication with Putin will remain open, but Berlin is girding for a long standoff, akin to a second Cold War.
"I think we need to prepare ourselves for a prolonged conflict in which Russia will use all the means at its disposal," Norbert Roettgen, chairman of the foreign affairs committee in the German Bundestag and a member of Merkel's conservative party, told Reuters.
"We are essentially in a waiting game," said another German official, who requested anonymity because of the sensitivity of the matter. "All we can do is keep an eye on the violence in eastern Ukraine and be prepared to react to it," he added.