Anthony Hamilton and Ryan Day have tested positive for coronavirus and withdrawn from the UK Championship.
The pair were due to face Xu Si and Jak Jones respectively on the first day of competition on Monday, with Xu and Jones now given byes to round two.
Hamilton withdrew from this year's World Championships at the Crucible as he felt that he was putting his health at risk.
Speaking in July, the four-time quarter-finalist said: "On a personal front I'm high risk - I've got asthma so I've been diligent to say the least during this lockdown.
"I've been shielding, basically. I haven't been seeing anyone. I've been practising on my own, I've been washing all my food, cleaning my clothes before going in the house, all that business.
"So to go into a room with 300 people is against the grain for me. I'm not going to be comfortable in there personally. I don't know why anyone is going to be comfortable."
However, Hamilton has played in subsequent tournaments, including losing in the first round of last week's Northern Ireland Open.
In a statement World Snooker said: "All other players and officials tested at the event so far have had negative results.
"Hamilton and Day will now undergo a period of self isolation and will receive the support of WST."