Humphries is suffering from gastroenteritis, commonly referred to as stomach flu. He will therefore be unable to compete or face Ryan Searle in the first round.
Cool Hand Luke has already won two major titles this year, the World Grand Prix and the World Cup of Darts, while he lost the finals of the World Masters and the Premier League.
Under PDC rules, Huybrechts takes his place in the field.
The Belgian narrowly missed out on qualification after finishing 33rd in the European Tour Rankings and now gets a second chance.
Level on points with Karel Sedlacek in 32nd, Huybrechts had won less prize money over the previous four tournaments and had also come off second best in their head-to-head record.