The 2018 Croatia Open Umag (also known as the Plava Laguna Croatia Open Umag for sponsorship reasons) was a men's tennis tournament played on outdoor clay courts. It was the 29th edition of the Croatia Open, and part of the ATP World Tour 250 Series of the 2018 ATP World Tour. It took place at the International Tennis Center in Umag, Croatia, from 15 July through 22 July 2018.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 United Kingdom | ||||
 Bosnia and Herzegovina | Damir Džumhur | 23 | 2 | |
 Italy | Marco Cecchinato | 29 | 3 | |
 Russian Federation | Andrey Rublev | 33 | 4 | |
 Spain | Albert Ramos Viñolas | 38 | 5 | |
| Robin Haase | 43 | 6 | ||
| João Sousa | 45 | 7 | ||
 France | Benoît Paire | 47 | 8 | |
| Maximilian Marterer | 48 | 9 |
The following players received wildcards into the singles main draw:
The following players received entry from the qualifying draw:
The following player received entry as a lucky loser:
Kyle Edmund → replaced by 
Andrej Martin Guillermo García López → replaced by 
Laslo Đere Filip Krajinović → replaced by 
Taro Daniel Andreas Seppi → replaced by 
Guido Pella| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| United Kingdom | Dominic Inglot | Franko Škugor | 67 | 1 | ||
| Robin Haase | Matwé Middelkoop | 77 | 2 | |||
| Antonio Šančić |  Belarus | Andrei Vasilevski | 129 | 3 | ||
| France | Jonathan Eysseric | France | Hugo Nys | 133 | 4 |
The following pairs received wildcards into the doubles main draw:
The following pair received entry as alternates:
See main article: 2018 Croatia Open Umag – Singles.
Marco Cecchinato def. Guido Pella, 6–2, 7–6(7–4)See main article: 2018 Croatia Open Umag – Doubles.
Roman Jebavý / Jiří Veselý, 6–4, 6–4
