Six-year-old Adam King, who made headlines with his 'virtual hugs' late last year, has suffered a fractured femur.
Adam has brittle bones, and an update on his condition was posted on his Twitter page on Sunday night.
It says: "So a little personal post. As you know Adam has brittle bones and sadly he suffered a femur fracture this weekend.
"Thankfully he does not require surgery this time.
"He is happy to be home but he is very sore. Please keep him in your thoughts."
— Adam King Adventures (@AdamKingIRL) April 4, 2021
His family also praised staff at Cork University Hospital (CUH) "for the professionalism, care and genuine love shown to Adam".
The post adds: "We may be a little quieter on here for a few days".
Adam rubbed shoulder with the stars in December, when he got advice from real-life astronaut Chris Hadfield.
He was surprised by the spaceman, who tweeted following Adam's appearance on the 'Late, Late Toy Show'.
Chris asked him where he went on his space missions.
Flanked by his brothers and sisters, Adam replied: "Sometimes I go to the Moon, and sometimes I go to some other places like different planets".
Chris said when he was Adam's age, he and his siblings "did exactly the same thing".
Adam then asked Commander Hadfield if he was "afraid" on his first space mission.
He told him: "When I was six-years-old I was afraid because I didn't know everything that I needed to know yet.
"But I changed who I was, Adam - I studied and I read books, and I watched movies and I talked to people who knew what they were doing."