Robbie Williams entered a US rehab clinic on his 33rd birthday

Mark Owen said: "I'm so worried about him. I'm gutted and devastated things have ended up like this. I think he should come back to the UK."

And fellow pop star Howard Donald said in the interview with Reveal magazine: "I've been calling him loads.

"I'm upset some people think it's our success that's made him depressed."

Williams entered a US rehabilitation clinic on his 33rd birthday and missed last week's Brit Awards, where Take That won best single.

Take That's hit Patience won the Brit Award for best single

Owen said: "When I heard about him checking into rehab, I felt really sad - I just want him to get happy again.

"I'll do anything I can to help him. If he wants me to see him, I'll be straight on that plane."

"Me and Rob went through a period where we didn't speak," he added. But Williams got in touch after Owen won Celebrity Big Brother in 2002 and the pair have spoken about three times a week since.

"Rob was always my mate and I always felt very close to him," Owen said.

By Williams' standards, his latest album Rudebox had a disappointing reception, while his former group have enjoyed a hugely successful comeback without him.

Their new album Beautiful World sold 1.15 million copies in the UK in 2006 - compared with 454,000 for Rudebox.

Williams was only nominated for one Brit Award - for best live act - and did not win, while Take That picked up best single for Patience.

Owen also said comments about Williams at the Brits from host Russell Brand and Oasis star Noel Gallagher were uncalled for.