Canadian crooner Michael Buble was once so paranoid about his fertility he took a medical test to ensure he could have children.

The Home hitmaker's model wife Luisana Lopilato is pregnant with the couple's first child, but Buble admits he was once worried he would not be able to reproduce.

Buble tells ET Canada, "I went and got tested, because I was so sure it wasn't going to work."

The star also admits that although he is not "freaked out" by his impending fatherhood, he is "not ready" and adds, "But who knows who is ready?"

Buble and Lopilato wed in 2011 and announced their baby news earlier this year (Jan13).