Anatoly Chubais, 67, once also the Kremlin chief of staff, is the most senior official to have walked out on Putin and was pictured for the first time in Tel-Aviv.
Ukrainian President Volodymyr Zelenskiy has said that if Moscow holds referendums in occupied areas of his country on joining Russia, there could be no talks with Ukraine or its international allies.
Post-Soviet reformer Anatoly Chubais, who left Russia following Moscow's invasion of Ukraine, has reportedly been discharged from a hospital in Italy where he was being treated for a rare immunity disorder.
Authorities in Italy are examining the case of a former senior Russian official who was hospitalized in Sardinia this week after suffering neurological symptoms.