Richard Dreyfuss has been diagnosed with viral bronchitis

In a video shared on the SharkCon Instagram page, Richard said: "Hello cons, I'm very, very sorry to tell you that I've been diagnosed with viral bronchitis. And I've been told by my doctors I cannot fly, and I would have to fly five hours to get there.

"I'm terribly sorry because I had planned to be there and had been looking forward to it."

The themed event - which is being sponsored by National Geographic - is being held in Florida this weekend.

In his video message, Richard explained that he "didn't want to get anyone else sick".

The award-winning actor said: "I feel terrible about not showing up, and I'd feel worse about exposing you to this apparently very viral illness. But there will be other times and I will make it my business to show up and I want to wish you all good luck and happiness."

Richard also admitted to being "in a lot of pain" and insisted that his health was his top priority.

The Stand by Me star jokingly added: "I want you all to feel very sorry for me. And very sorry for yourselves. I'm in a lot of pain, and that has to come first, my health, and I feel very good about having the time and enough health."

SharkCon has also offered an apology to fans.

The convention said in a statement: "All prepaid autographs and photo ops will automatically be refunded. There is no reason to reach out.

"It will take 5-10 business days plus what your bank takes for them to be processed. We are so sorry for any inconvenience. Thank you."

Hollywood star Sharon Stone has already expressed her support for her showbiz pal, encouraging Richard to "give [her] a hug".

The 67-year-old actress wrote online: "Honey, feel better. The world is not good without you then come over and give me a hug."