Justin Bieber injured his neck falling down a flight of stairs.

The 19-year-old pop star took a tumble before a photo shoot for sportswear giant Adidas, leaving him with grazes on his neck.

He was not badly hurt in the accident, and the 'Boyfriend' singer posted a video on Instagram of him talking about the incident and showing his followers his neck.

In the clip, Justin - who was wearing a red baseball cap and white T-shirt - says: ''So I decided I was gonna fall down the stairs. So I did. So that's exactly what I did!''

The clip was captioned ''#whyigottafallandcutmyneckbeforeaphotoshoot fun''.

It seems Justin was able to see the funny side of his misstep, posting on Twitter: ''If u didn't hear I fell down the stairs this morning. Check my Instagram for details. It was epic :) lol (sic)''

Meanwhile, the teen idol set tongues wagging last week when he was spotted out at a basketball game with a mystery blonde in Miami, Florida.

The pair hid out in a private suite to watch the game between the Miami Heat and the San Antonio Spurs.

And insider told Hollywoodlife.com that the reason Justin wanted to be incognito was because he was afraid sports commentators would mock his outfit.

At a previous game pundits had laughed at his choice of attire.

The insider said: ''He didn't want to be made fun of on sports radio and SportsCenter - like he was last time at the Game 7 for the Indiana Pacers series - for what he was wearing, because he was pretty much wearing the exact time thing.''