The ER actor, 62, reflected on his friendship with Perry after he died in October aged 54.

He told US publication Deadline: "I knew Matt when he was 16 years old. We used to play paddle tennis together. He's about 10 years younger than me. And he was a great, funny, funny, funny kid.

"He was a kid and all he would say to us, I mean me, Richard Kind and Grant Heslov, was, 'I just want to get on a sitcom, man. I just want to get on a regular sitcom and I would be the happiest man on earth'. And he got on probably one of the best ever," Clooney said.

The pair shot to fame at the same time, with ER and Friends both debuting in 1994 and airing on Thursday nights in the US. Clooney said they were "side-by-side on the soundstage".

"Watching that go on on the lot - we were at Warner Brothers, we were there right next to each other - it was hard to watch because we didn't know what was going through him," Clooney added.

"We just knew that he wasn't happy and I had no idea he was doing what, 12 Vicodin a day and all the stuff he talked about, all that heartbreaking stuff."

"And it also just tells you that success and money and all those things, it doesn't just automatically bring you happiness. You have to be happy with yourself and your life."

Read more:
What Perry's memoir revealed
Obituary: The one who made everyone laugh
Perry's life in pictures

A post-mortem ruled Perry's death as an accident from the "acute effects of ketamine".

Perry, best known for playing wise-cracking Chandler Bing in Friends, was found unresponsive in the swimming pool at his LA home on 28 October and pronounced dead at the scene.

Other contributing factors to his death included drowning, coronary artery disease and the effects of buprenorphine, which can be used to treat opioid use disorder, officials said.