A lonely Labrador who was dubbed the 'saddest dog in the world' faces being put down in a week after she was rejected by a second family.

Lana's plight touched the hearts of millions of dog lovers in 2015 after a photo of her looking depressed in her kennel when her foster family returned her went viral.

After 4,000 adoption applications and $15,000 in donations to cover her care, the two-year-old pooch finally found a second home in Ontario, Canada, in January 2016.

But the new owners ditched her just months later - and the desolate dog now faces being euthanized on May 20 after her third birthday unless she can find a home.

Lana the Labrador's plight touched the hearts of millions of dog lovers in 2015 after a photo of her looking depressed in her kennel (pictured) when her foster family abandoned her went viral

She now faces being put down after she was rejected by a second foster family (pictured now)

'May 14 is Lana's birthday (she will be three),' Canadian non-profit Rescue Dogs Match wrote in a desperate appeal on Facebook last week.

'Please help find her a foster or forever home. Lana only has until May 20th.'

She is currently at a boarding facility which is getting overcrowded, meaning they no longer have the room to keep Lana.

The Labrador may be put to sleep since she has not been able to find a permanent home for three years.

Lana first arrived at a boarding kennel in Toronto as a puppy – the runt of a large litter in Mexico.

She was kept in a foster program, spending short amounts of time with different families with no problems reported.

Eventually she was placed with one family permanently at five months old, but they returned her in October 2015 after her guarding issues resurfaced.

Lana was the 'size of a hand' when she first arrived at a boarding kennel in Toronto as a puppy – the runt of a large litter in Mexico

She was adopted by a family in 2015 - but they returned her after she snapped at the mother just once while protecting her food. Once returned to her kennel she was so heartbroken she refused to move or go on walks (pictured)

Rescue worker Dahlia Ayoub (pictured with Lana) said the pooch was soon back to her old self and was happy to see her the following day

Dahlia Ayoub, of Mighty Mutts, explained that Lana was the size of her hand when she arrived at the kennel and 'terrified' of everything.

She added that the only time her guarding instincts, stemming from when she was forced to compete for food with her siblings, have only reappeared that one time.

'She snapped at the mom. And they decided because they have kids in the house to bring her back to boarding.'

When her new owners returned her to the kennel, she said Lana was unresponsive for a whole day and too heartbroken to move or go on walks.

'It's almost like her world shut down,' she told The Dodo.

But Lana was soon back to her old self and was happy to see the rescue worker the following day.

After 4,000 applications to adopt her and $15,000 in donations to cover her care, the two-year-old pooch finally found a second home in Ontario, Canada, in January 2016

But unbeknownst to Lana's millions of fans, they returned her to the shelter in July, because they realised she was not the kind of dog to be petted and given belly rubs, but one that preferred having a job and being outdoors (pictured at her first foster home)

Lana's story seemed to have a happy ending when a second family adopted her in January 2016.

But unbeknownst to Lana's millions of fans, they returned her to the shelter in July.

'Lana's adoption did not work out because people want a dog they can pet and play with,' Brenda Dobranski, founder of Rescue Dogs Match, told The Dodo.

'Lana is a silly fun girl but she is not the type of dog that will let you give belly rubs to and sleep in bed with. She loves to have a job.'

She went to a boarding shelter until October 2016.

Then she was placed in a foster home for a week, before going to another boarding house in November 2016 - which needs her out by May 20.

'We need to keep Lana's happiness and well being at the forefront,' Ms Dobranski said. 'It is not fair for her to have to keep moving around.'

Ms Dobranksi explained that every time she settles in one place she is uprooted again - leaving her agitated.

The desolate dog now faces being euthanized by May 20 after her third birthday unless she can find a home due to overcrowding at the kennel where she is staying

'The best environment for her would be a horse or hobby farm where she can be outside most of the time "helping" her person with the chores around the property,' Rescue Dog's Match explained

The non-profit added that the ideal family would be a mature couple or someone with the 'time, patience, determination and commitment to help her become more confident'

'The best environment for her would be a horse or hobby farm where she can be outside most of the time "helping" her person with the chores around the property,' Rescue Dog's Match explained.

'She loves to be outside no matter what the weather. Lana loves to be part of whatever is going on but not in 'tight' quarters.'

The non-profit added that the ideal family would be a mature couple or someone with the 'time, patience, determination and commitment to help her become more confident'.

Lana's chances of adoption are slimmed down by the fact that she must be adopted by a family in Canada.

They are hoping that Lana's match would have a routine she could rely on and an active lifestyle that would 'banish the thought of endless hours in concrete bunkers with nothing to do'.

Lana was described as 'sweet and silly' but has a 'tendency to shut down' when she is not around people she trusts.

'It is important for her to be in a home where she will continue to be exposed to new situations with lots of positive reinforcement,' Rescue Dog's Match concluded.

'She is loyal and loving to the people she trusts.'

Her rescue team was said to be 'committed' to supporting Lana and hopefully finding a family with the training and time to ensure her third home is her last.

Please email info@rescuedogsmatch.com if you are interested in fostering or adopting Lana