However, Grybauskaitė said that Trump's remarks on social media do not necessarily signal changes to the US policies.
"What is said online will not necessarily be fulfilled and we have already heard the US ambassador's speech about Ukraine at the United Nations. It's exactly what we think about the situation. So, I think that we need to focus more on ourselves and react less to what is said online," she told reporters in Malta.
The Lithuanian president described Trump's behavior as "Twitter diplomacy".
According to Grybauskaitė, the EU will have "to learn unconventional diplomacy, to see and read what is given to us online, and to focus more on ourselves, to take more responsibility for Europe's future".
Highlighting the level of concern, European Council President Donald Tusk on Tuesday described Trump, along with Russia, China, Islamic extremism and domestic populism, as the biggest "threats" to the bloc in its 60-year history.
Grybauskaitė said that Tusk's statement was his "personal opinion".