Daniel Radcliffe missed an appearance at San Diego Comic-Con on Thursday (24.07.14) because of a ''visa glitch''.

The 'Harry Potter' actor was stopped from flying from Toronto in Canada to the annual festival in California because he needed a stamp on his recently updated visa but computers were down at the US Embassy.

A source told the New York Post newspaper's Page Six column: ''He's stuck in Toronto with visa problems.''

The publication reports Daniel, 25, recently updated his visa from a P-2 visa - designated for foreign actors and entertainers - to an O-1 visa for ''the individual who possesses extraordinary ability in the sciences, arts, education, business or athletics''.

But he then ran into difficulties after promoting his movie 'What If' in Toronto earlier in the week.

The source explained: ''Daniel needed a stamp from the US embassy in Toronto to travel back to the States. And their computer system was down.''

It is unclear if he will make it to Comic-Con in time for a panel today (25.07.14) with the cast and director of his new movie 'Horns', in which he plays a man who grows horns after possibly killing his girlfriend.