"Unfortunately the human interest side of this is enormous now and that's been very difficult."
He said he did not feel it was necessary to have Madeleine's image constantly in the news.
"We cannot sustain that level of interest and Kate and I want to withdraw from the campaign," he explained.
They have made no final decision on when to return home but Mr McCann said he thought staying in Portugal might have become counter-productive.
"But the very real difficulty is the emotion of leaving Portugal as a family of four when we went there as a family of five."