The post was accompanied by a photo of a dog wearing Mickey Mouse ears.
Hours later, Steve shared another image – a test strip showing a positive Covid result alongside a negative flu result – with the caption: “Hey! No flu!”
Ticket holders will receive refunds for the cancelled performances, according to promoters.
Fans sent well wishes in the comments of Steve’s posts.
One wrote: “I hope you feel better very soon, Steve. Take extra care of you.”
Another said: “Please come back when you feel better. I’ve wanted to see you in person for over 40 years.”
The pair are next due to appear in Florida on October 4 – a rescheduled date from January, when Short tested positive for Covid.
The tour is expected to continue with stops in Las Vegas, Boston, Pittsburgh and Austin, before concluding in Cleveland in April 2026.
Martin and Short attended the Emmy Awards last Sunday with their Only Murders in the Building co-star Selena Gomez.
Now in its fifth season, the Hulu series continues to release weekly episodes.
The show received seven nominations at this year’s ceremony, including an acting nod for Martin, but did not win any awards.
Since its debut it has been nominated 56 times, winning seven trophies.
The comedy features Martin, Short and Gomez as New York neighbours Charles-Haden Savage, Oliver Putnam and Mabel Mora – all amateur sleuths drawn into a succession of grisly murder investigations.
Season five introduces new guest stars Renée Zellweger, Keegan-Michael Key, Christoph Waltz and Logan Lerman.
The first three episodes premiered on September 9, with subsequent instalments released every Tuesday.