German umpire Ben Goentgen was suffered a cheek bone fracture after being hit flush in the face from a penalty corner deflection during the Netherlands and South Korea match.
Goentgen will undergo surgery on Thursday after being diagnosed, the FIH said.
Goentgen had little time to react during the incident due to the shot originally coming from the dragflick of South Korean Jang Jonghyun which deflected off a Dutch stick.
The German immediately fell down in pain while his co-umpire Gareth Greenfield rushed to help.
There was a five-minute delay as medical attention was sought and a replacement onfield official could take over.
He was eventually replaced by Indian reserve umpire Raghu Prasad.