One Direction are ''fully understanding'' of Zayn Malik's decision to take a break from the band's tour.

It was confirmed earlier today (19.03.15) that the 22-year-old singer had been ''signed off with stress'' and had flown back to the UK but his bandmates - Harry Styles, Liam Payne, Niall Horan and Louis Tomlinson - are said to be ''stunned'' but fully ''supportive'' of Zayn's decision.

An insider shared: ''The boys fully understand Zayn's desire to leave their current tour.

''They were a little stunned at first, but realise it's for the best with everything he's going through with Perrie and the long-tour commitment, which really takes it out of you.

''It's up to them now to carry the torch while Zayn does what he needs to do, and they're up for the challenge of becoming a four-piece, instead of five. Harry, Liam, Niall and Louis are very supportive of Zayn's need to recuperate and get his life back on track. They're like brothers and will do anything they can to help.''

The 'Night Changes' hitmaker has reportedly been left stressed by the media speculation surrounding his private life after he was photographed with a woman whilst partying in Phuket, Thailand.

Meanwhile, Zayn's decision to leave his bandmates in Asia was reportedly the direct result of an ''ultimatum'' given by his fiancée Perrie Edwards.

A source told HollywoodLife.com: ''She was furious about the pictures of him holding hands with an attractive blonde fan, and delivered an ultimatum to leave the tour and fix their relationship.

''Zayn's been away on a world tour and it's difficult for them to maintain their commitment when they aren't together. Perrie reiterated, 'Get home if you want to sort this mess out, or we're done.'''