"Refusing to participate in the military committee means that there are some very difficult processes going on inside the country," he said during an address on YouTube.
Soskin added that disagreements could arise between Zelensky and top military leaders.
"This is an unprecedented event ... It will have serious consequences," he said.
Earlier, Secretary of the National Security and Defense Council of Ukraine (NSDC) Oleksiy Danilov said that Kiev does not yet have a final plan for a counteroffensive.
Mykhailo Podolyak, adviser to the head of the office of the Ukrainian president, also urged not to consider the planned offensive of the Armed Forces of Ukraine as the only battle that will determine the entire course of hostilities.
Ukrainian Foreign Minister Dmytro Kuleba admitted that if the counteroffensive is unsuccessful, Kyiv will try to organize a new one.