He said: "I would want a woman to call me if I hadn't called her. If I don't call it's because I'm busy. But this is why I'm single. But there is also the element that the second you think a girl is maybe not quite as keen, there is a little more interest in the situation. Sometimes, when it's there right in front of you, it's not as interesting."
The Scottish-born actor previously revealed is gets "paranoid" about having sex now he is famous.
The 41-year-old Hollywood hunk is worried potential partners will publicly reveal any bedroom liaison and so he is much more cautious about his behaviour.
He said: "I get laid less now than I used to, because I'm way more paranoid now. I'm nowhere near as naughty as I used to be, partly because I did a lot of that when I was drinking."