The post went on to ensure all ticket holders will be notified via email regarding the rescheduled shows.
Guy also shared a personal statement following the news, writing: "I am absolutely gutted! I was so looking forward to performing in Cairns and Townsville next week. I am so sorry to disappoint my fans and I promise to do something even more special once I'm able to perform as a thank you for your patience and understanding."
It didn't take long for the Choir singer to be inundated with support from his fans and friends.
"Get better soon Guy 😘," Voice host Sonia Kruger commented on the post.
Dannii Minogue also sent her well wishes, writing: "I hope you get better 🙏🏼 that is such a heavy feeling having to cancel a show 😩."
Responding to all the love, Guy said he was "blown away" by the kindness, while also sharing a health update.
"I only felt a little sick when I tested + earlier today but starting to feel pretty crook now. Hopefully it passes quickly."
WATCH: Guy Sebastian apologises for "promoting vaccines" (Article continues after video)
The singer's COVID diagnosis comes eight months after he faced backlash for withdrawing his support for the #VaxTheNation campaign, which encouraged Australians to get the COVID vaccine.
Initially promoting his involvement in the industry-wide campaign, alongside names such as Paul Kelly and Jimmy Barnes, Guy soon reneged on his support, saying that the original post had been published without his “direct involvement”.
"Whilst I want things to get going again, it’s not my role to communicate in the way that post was communicating," he said in an apology clip.
He continued: "I would never, ever tell people what to do when it comes to their personal health choices.
"I’m very sensitive of it, not only on a public level, but even in my personal life with people who have circumstances that they have to consider when making these choices," he concluded, adding that he was "really sorry".
"It was not a post that communicated with love or compassion, which I feel is what’s needed when it comes to addressing things like vaccinations."
The Australian Idol alum later confirmed to news.com.au that he himself is "double-vaccinated", but he doesn't believe it's his place "to tell people what to do".