The 29-year-old cut his eye as he tried to take out a contact lens and it has now become infected.
The United States international is set to see a specialist over the injury as he cannot see out of the eye.
"It was a freak thing," DeMerit told the Daily Mail. "It got worse and worse and I still can't see out of that eye.
"Scar tissue is starting to develop, which is blurring my vision, so I'm seeing a specialist and I might have to have surgery."
Watford 11/10, Draw 9/4, Coventry 13/5