The chart showed that Serbia declined to provide training to Ukrainian forces, but had committed to sending lethal aid or had supplied it already.
It also said Serbia had the political will and military ability to provide weapons to Ukraine in the future.
The Pentagon also did not immediately respond to Reuters questions about the document's reference to Serbia and has previously declined to comment on any of the leaked documents.
Vucic's government has professed neutrality in the Ukraine war, despite the country's deep historic, economic and cultural ties with Russia.
"We didn't export any weapons or ammunition to Russia or Ukraine," he said during a March 5 visit to Qatar.