Pop star Justin Bieber was left nursing a neck injury on Sunday (23Jun13) after falling down a flight of stairs. The Baby hitmaker took a tumble on a day off from the U.S. leg of his Believe tour, and uploaded a photo of his grazed skin to his Instagram.com page. Explaining the injury to fans in an online video, Bieber joked, "So I decided I was gonna fall down the stairs... so I did! That's exactly what I did." The 19-year-old singer, who was due to take part in a photoshoot for Adidas, also wrote, "Why I gotta fall and cut my neck before a photoshoot... fun." Bieber is next due onstage in Los Angeles on Monday (24Jun13).