The future of the world’s biggest boyband One Direction could be in doubt, following a difficult week for the group which culminated in Zayn Malik leaving their 'On The Road Again' tour due to stress. The singer, who is engaged to Little Mix’s Perrie Edwards, had been accused of cheating on his fiancée last week, while the band were on tour in Asia.

Zayn MalikZayn left the 1D tour on Thursday

Zayn’s departure from the tour was announced on Thursday by the band’s publicist Simon Jones who delivered the news on Twitter writing, "1D statement: Zayn has been signed off with stress and is flying back to the UK to recuperate. The band wish him well and will continue with their performances in Manila and Jakarta.” The 22 year old has since been spotted arriving home to Heathrow.

Following the publication of pictures showing Zayn with his arms around another woman the singer initially told his twitter followers on Wednesday, "I'm 22 years old... I love a girl named Perrie Edwards. And there's a lot of jealous f--ks in this world I'm sorry for what it looks like.”

More: Zayn Malik "Signed Off With Stress", Taking A Break From One Direction Tour

A source close to Zayn the rest of the band has since told E! News that the singer’s issues are purely personal and not due to a wider problem within the group. "He gets on with everyone, so this is nothing to do with a bigger problem within the band. They are all good," the source said.

"But Zayn is a very artistic person. He's passionate and sensitive. And he can be quite shy. Being on tour can be hard. And being under the spotlight can be difficult. When you are on the road it can be hard to turn it off.  He is very close to his mom. It's good that he is able to take a breather. Ultimately he is a really lovely guy. I wouldn't read too much into this.”

One DirectionZayn and his One Direction bandmates

The source added that since the group’s formation in 2010 the singer has struggled with fame. "He is just a kid. He wants to make music, but the spotlight that comes with it is hard," the insider said.

"Fame is kind of catching up with all if them. It's been a gruelling and intense few years and it's having a snowball effect now. Zayn would be happy with a low-key life. He has a problem with the fame—he doesn't handle the attention very well, and every so often he has a little wobble.”

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But following Malik’s exit from the tour bookies have slashed odds on the band breaking up in 2015. Odds on a 1D split have now gone from 8/1 to 4/1, according to The Mirror.

"It looks like it's the beginning of the end for One Direction,” Ladbroke’s Jessica Bridge told The Mirror. “Zayn’s not the only one stressed out at the moment, but the odds suggest this could well be their farewell tour."