According to RTE Ten, Horan's knee was injured after the incident in Amsterdam Wednesday night when the projectile from the crowd struck him.

He later took to Twitter to (gently) tell off those involved, as well as make a plea to other fans to watch what they throw onto the stage. "Also guys!" he tweeted. "Can you limit what gets thrown on stage please! Coz somethin thrown at me tonight! Hit my knee! A lot of pain from it!"