Hopp wasn't due to play until tonight at the UK Open anyway as part of the World's Top 32 seeds who will take on those who won through from the third round.
Despite that, he has glandular fever and as a result has had to withdraw from the tournament. This means that a bye will be given later on in the fourth round draw which will take place on the Main Stage at the conclusion of the afternoon session.
https://twitter.com/OfficialPDC/status/1235867092483620865?s=20