See main article: article and 2021 Croatia Open Umag.
Robin Haase and Philipp Oswald were the reigning champions from when the tournament was last held in 2019,[1] but chose not to defend their title.
Fernando Romboli and David Vega Hernández won the title, defeating Tomislav Brkić and Nikola Ćaćić in the final, 6–3, 7–5.