The 2021 Croatia Open (also known as the Plava Laguna Croatia Open Umag for sponsorship reasons) is a men's tennis tournament played on outdoor clay courts.

It is the 31st edition of the Croatia Open, and part of the 250 Series of the 2021 ATP Tour.

It take place at the International Tennis Center in Umag, Croatia, from 19 through 25 July 2021.

[1][2] *per team The following players received wildcards into the main draw: The following players received entry from the qualifying draw: The following player received entry as a lucky loser: The following pairs received wildcards into the doubles main draw: