The Irish guitar player, who underwent surgery on his knee in January, asked fans to be more careful about throwing items on stage as they are causing the boys injuries.
"I honestly think that last night's crowd in Amsterdam was one of the loudest One Direction crowds yet! The place was rockin! Thanks Holland," wrote Niall before adding, "Also guys! Can you limit what gets thrown on stage please! Coz somethin thrown at me tonight! Hit my knee! A lot of pain from it!"