One Direction singer Niall Horan was injured during the group's concert in Amsterdam Wednesday night by a heavy object, presumed to be a shoe, that was thrown on stage. Horan, 20, who was struck in his knee, is still recovering from a knee operation in January.

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After the incident, Horan was struggling to walk and eventually limped his way offstage. Later Horan took to Twitter, where he posted his thanks to fans for coming to the show. He also tweeted: "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!"

Harry Styles, also 20, was hit in the face by a flying object from the crowd, but he continued to perform.