Mike’s celebrity friends sent get well soon messages, with Joe Jonas wroting: “Rest up bro. Glad you are OK.”
Millie Bobby Brown said: “What!!! Get well soon, sending best wishes to you.”
And Jessie J commented: “You are a real life super hero.”
Mike embarked on a hike across the US in April, starting in Asbury Park, New Jersey.
He plans to walk 20 miles a day, reaching California in September.