He found time to paint his nails, but Chris Martin appeared to have forgotten one important thing before leaving the house earlier this week – his wedding ring.

There was no disguising the Coldplay singer despite him being wrapped up in a Michelin-style jacket and donning a hood as he rode his mountain bike near the couple's north London home.

Aside from his distracting coloured polish, all eyes were on the empty space where his wedding band usually is, fuelling speculation about his four-year marriage to Gwyneth Paltrow.

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Spinning around: Chris Martin crusing around London's Primrose Hill on Wednesday

Seeing red: Chris wore coloured nail polish - but no wedding ring

Friends of Speed of Sound star, who has two children with the Oscar-winning actress, say the marriage has been under a lot of stress lately as they both try to juggle wildly successful careers with family life.

In the past five years, Paltrow has taken a backseat in her Hollywood career, appearing in only a clutch of films as she concentrates on being mum to three-year-old Apple and two-year-old son Moses.

However in recent months, the 35-year-old actress has resumed her A-list career, while Martin is currently working hard on his upcoming fourth album due out in May.

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Family matters: Chris has been married to Gwyneth Paltrow, 35, for four years. The couple have two children together, Apple and Moses

"This has been a very strenuous period for Gwyneth and Chris," a source told Mail Online.

"They have been apart almost as much as they have managed to be together, and with her going off in one direction, and him in another, there has been little time for them to spend together and it's taking a toll on their relationship.

"Chris really wants his new album to do well,' says the source. 'So he has been putting in long hours at the recording studio writing songs, and working on melodies.

"And Gwyneth just completed two back to back films, Two Lovers, with Joaquin Phoenix, and Iron Man with Robert Downey Junior.

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Ring: Chris showed off his wedding band during a Live 8 performance in 2005

"On top of that, she recently teamed up with Jemima Khan and Sir Roger Moore to produce a four minute film for Unicef, on babies with HIV."

The source adds that Paltrow attended Ashton Kutcher's 30th birthday alone at club Socialista in New York earlier this month.

According to the source, the couple have also been talk about adding another child to their family, with Matrin wanting to act on the new addition now, while Paltrow feels she would like to wait until their lives calm back down again.

"Both Gwyneth and Chris have talked about having another child of their own, but recently, Chris has been talking about adopting a child from another country.

"While Gwyneth loves kids, she feels they have their hands full right now, and seldom get to spend time together as it is, and she'd like to put plans to add to their family on hold."

Recently speaking at a Malawi benefit concert, Paltrow said, "We might get one (a baby) from Brooklyn. My husband wants to adopt, so I don't know. I am sort of open."