The 24-year-old actor had revealed in 2012 having a "massive crush" on the 'Roar' hitmaker, reported the Huffington Post.
"Mentally I am very close to Katy Perry a lot. I've been in a room with her since and I couldn't say (anything). I was like across a room from her and I was like, 'I can't," Radcliffe said.
"I just can't even say anything. You've probably seen an interview with me. You know these thoughts are in my head. I can't even look at you," he added.