George Clooney is said to have been forced to scale back his commitments at the Venice Film Festival after falling ill on the opening day

Insiders told The Hollywood Reporter George began to feel unwell in the afternoon and was advised to return to his accommodation to rest ahead of Thursday's press conference and world premiere.

The actor was photographed leaving the Hotel Excelsior by boat at around 4pm.

His absence meant he missed a dinner with director Noah Baumbach, 55, and co-stars Adam Sandler, 58, and Laura Dern, also 58.

The nature of his illness has not been disclosed, but sources have stressed it was "nothing to worry about".

Hours earlier, George had been seen arriving at the Lido with Laura, dressed in a navy suit, striped shirt and tinted sunglasses.

George's health scare comes after he recently discussed his future plans in acting.

In March, he told CBS News programme 60 Minutes he would no longer appear in romantic comedies.

He said: "Look, I'm 63 years old. I'm not trying to compete with 25-year-old leading men. That's not my job. I'm not doing romantic films anymore."

He was speaking ahead of his Broadway debut in Good Night, And Good Luck, an adaptation of his 2005 Oscar-nominated film of the same name.

George plays journalist Edward R Murrow in the stage production, which recounts Murrow's televised confrontation with Senator Joseph McCarthy during the "Second Red Scare" of the 1950s.

He said: "It's exciting to be (on Broadway.) Let's not kid ourselves. It's nerve-wracking. And there's a million reasons why it's dumb to do.

"It's dumb to do because you're coming out and saying, 'Well, let's try to get an audience to take this ride with you back to 1954'."

Reflecting on the relationship between government and the press, George said: "We're seeing this idea of using government to scare or fine, or use corporations to make journalists smaller.

"Governments don't like the freedom of the press, they never have. And that goes for whether you are a conservative or a liberal or whatever side you're on. They don't like the press."

The lifelong Democrat also spoke about his decision to call on Joe Biden, 82, to step aside from the last U.S. presidential race after his debate with Donald Trump, 79.

George said: "I was raised to tell the truth. I had seen the president up close for this fundraiser, and I was surprised. And so, I feel as if there was a lot of... cowardice in my party, through all of that, and I was not proud of that, and I also believed I had to tell the truth."