The A-Team hitmaker wrote several tracks for the British boyband's second album Take Me Home, and was approached to help them with their third album.
Sheeran admits he turned down the offer because he wants to concentrate all his songwriting skills for his own upcoming second record.
He tells MTV.com, "I haven't done any songs on this one. I've actually kind of cut myself from giving any people songs at the moment, because I want to make my album. I was approached, and it wasn't so much a 'No'. it was just a 'I want to write tunes for myself at the moment.'"