The 52-year-old actor-turned-singer has been forced to cancel the three remaining dates on his current European tour after injuring his ribs in a freak accident.
He wrote on Instagram: "Sadly I slipped on the steps of the tour bus whilst travelling to Denmark and seriously injured a rib, making it difficult to breathe and impossible to sing.
"Regretfully, I will not be able to perform the last 3 shows on our tour, but have every intention of making these shows up in September/ October when we return."
The 'Designated Survivor' star went on to apologise to the fans who had tickets to see him perform in Denmark and Sweden and vowed to make it up to them.
He continued: "I am so sorry for any inconvenience that I've caused to the fans who have bought tickets.
"I will do everything I can to make it up to you.
"Thank you for your understanding."
Meanwhile, Kiefer recently admitted he hasn't watched "a single" TV show or film he has starred in since his 1986 movie 'Stand By Me' -in which he played Ace Merill - because he "only sees himself" and finds he "gets in the way" of the overall plot of the project.
He said: "Since 'Stand By Me' I don't think I've watched a single thing I've ever done.
"Because when I would watch a movie or a television show that I had done I would only see myself.
"I would kind of get in the way, so I just stopped watching a long, long time ago.
"So I'd never really watched '24' unless there was a real problem or something that we had to deal with."