The actor, who plays fisheries expert Alfred Jones in the romantic comedy, said fishing was not one of his favourite hobbies.
The film, which has been adapted from Paul Torday's novel, sees McGregor tasked with the seemingly impossible mission of introducing salmon into the Yemen wadis by a sheikh.
"I'm not really a fisherman," he said.
"I must have done some fishing when I was a kid here and there but it is not really a passion of mine."
McGregor and co-star Emily Blunt walked the sodden red carpet at the UK premiere of the film in Kensington, London.
Dozens of fans braved rain and sleet to get a glimpse of the stars.
McGregor said that working alongside Blunt was "fantastic".
He said: "She is a great partner to have in a movie. She is a lovely woman, she is funny. She has a wicked sense of humour.
"There is something very similar about the way we approach our work and we threw ourselves into the scenes. We didn't have a great deal of discussion about what we were going to do before the camera was rolling and I like that the best."
Emily Blunt and Ewan McGregor hit the red carpet...