The United States and the European Union have consistently demanded Assad stand down in any peace deal.
But last week Washington signalled it would no longer focus on Assad's ouster as it concentrates on the wider fight against terror groups such as Islamic State.
Asked what this meant for EU policy, bloc foreign affairs chief Federica Mogherini said she believed it "would be impossible" to return to the status quo in Syria.
"But this is for the Syrians to decide, that is clear ... any solution that can be acceptable by all Syrians, we will support it."
Diplomatic sources said the foreign ministers are expected to endorse a statement which notes: "The EU recalls that there can be no lasting peace in Syria under the current regime."
Mogherini tomorrow co-hosts with the United Nations a two-day conference on Syria's future in Brussels focused on the disastrous humanitarian situation in the country after a war which has claimed more than 320,000 lives and displaced more than half the population.
German Foreign Minister Sigmar Gabriel said he believed the changed United States position was certainly "more realistic", as to insist that Assad must step down from the start would only result in deadlock.
"But there is one thing which cannot happen -- that a dictator who committed horrible crimes in the region remains untouched," Gabriel said.
"This cannot be abandoned or subordinated to the conflict against Islamic State," he added.
French Foreign Minister Jean-Marc Ayrault for his part said there had to be a genuine political transition to a new Syria.
"France does not believe for an instant that this new Syria can be led by Assad," he said.
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