"We have intel that Russia is preparing a new massive attack on our country – primarily targeting energy and logistics," Zelenskyy said in his nightly address.
"The assumption is basically that tomorrow the world will be watching the American midterms, and what is happening here in Ukraine, along with our difficulties with air defense and Patriot missiles, will be overlooked."
Zelenskyy's warning came hours after Russian forces struck a school being used to distribute humanitarian aid in Komyshuvakha, a settlement in southeastern Ukraine's Zaporizhzhia region.
At least 26 people, including police officers and first responders, were killed, five others were injured and others remained missing, according to the Ukrainian news outlet Steve Witkoff and Jared Kushner, both of whom have been involved in diplomatic efforts with Moscow.
Zelenskyy told Fox News in a Sunday interview that Ukraine would suspend strikes on Russian oil refineries for a month if Washington provided Patriot missile interceptors during the same period, potentially opening the door to diplomacy.
The State Department approved the potential sale of 500 Patriot PAC-3 interceptor missiles to Ukraine for an estimated $2.1 billion, according to Reuters.
The proposed sale could provide a significant boost to Ukraine's air defenses if finalized, although the delivery timeline is uncertain.
On Monday, Ukraine also accused Moscow of exploiting a U.S.-backed humanitarian ceasefire in Oleshky, in Ukraine's southern Kherson region, to strengthen Russian military positions.
Nearly 800 people were evacuated during the six-day humanitarian pause, according to first lady Melania Trump, with the White House clarifying that she helped broker the arrangement.
Ukraine's General Staff accused Russian forces of using the humanitarian pause to rotate troops, reinforce their defenses and improve battlefield logistics.
"Under the ceasefire introduced for the humanitarian operation in Oleshky, units of the Defence Forces of Ukraine ensured that the ceasefire was observed and acted exclusively within the framework of the agreements reached," the General Staff said in a statement on X.
"The enemy, by contrast, used the humanitarian pause to improve its positions."