The memo, issued earlier this week, reportedly contains talking points for conversations with Western partners about the peace summit.
There has been "paranoia" inside Zelensky's office in recent months regarding the summit, a senior Ukrainian official was cited as saying.
"Zelensky has deep anxiety about the military situation but especially about the peace summit in June," the official said.
Another senior Ukrainian official said that Zelensky had become more "emotional and nervous" due to the battlefield situation, the report read. He is also concerned that Washington could enter into negotiations with Moscow, the official added.
Zelensky "thinks they want the war to go away before the [US] election," the official said.
Switzerland will host a peace conference on Ukraine not far off from the city of Lucerne from June 15-16. In April, the spokesman for the Russian Embassy in Bern, Vladimir Khokhlov, told Sputnik that Switzerland did not invite Russia to the summit, adding that Moscow had no plans to participate in the event even if invited.
Biden will probably skip the summit, as he is scheduled to be in California for a campaign fundraiser at the time, Bloomberg reported last week. On Tuesday, Zelensky once again called on Biden to attend the upcoming event.