Justin Bieber is ''truly exhausted''.

The 23-year-old singer sparked concern for his health after he cancelled the final 14 dates on his 'Purpose World Tour' earlier this week due to ''unforeseen circumstances'', and a friend of the star has now claimed he is suffering from a ''mental exhaustion'' and needs time to rest.

The source said: ''He didn't feel like he could give the rest of the tour as much energy as his fans deserve. He is a perfectionist and didn't want to disappoint fans with some half-ass performance. He thinks his fans deserve and should expect the same performance at the end of the tour as in the beginning. He just didn't have that passion right now. He is truly exhausted.''

And whilst the insider insists this cancellation doesn't mark a permanent end to the 'Sorry' hitmaker's touring days, the star does need time to ''focus on [his] own mental health.''

They added to People magazine: ''It's a mental exhaustion that very few people understand. It seems very fair, although understandably disappointing to his fans, that he canceled the rest of the tour. It's a mature way of saying, 'Sorry, I need to focus on my own health for a bit.'

''It wasn't an easy decision for him. He has had this feeling before though and knows he has to just take a break from performing. It doesn't mean he will never tour again -- of course he will. He loves touring. Let the guy rest, and he will come back even better.''

Justin cancelled the remaining dates of his tour on Monday (24.07.17), after having spent an extensive 18 months on the road in support of his 2015 album 'Purpose'.

A statement released at the time read: ''Due to unforeseen circumstances, Justin Bieber will cancel the remainder of the Purpose World Tour concerts. Justin loves his fans and hates to disappoint them. He thanks his fans for the incredible experience of the Purpose World Tour over last 18 months. He is grateful and honoured to have shared that experience with his cast and crew for over 150 successful shows across 6 continents during this run. However, after careful consideration he has decided he will not be performing any further dates. Tickets will be refunded at point of purchase.''