Can being a loner be a sign of depression?

Loner: Possible, if accompanied by other signs of depression.

Is it new?: Many of us -- myself included -- enjoy work and play without a lot of other people necessarily being around. Einstein called himself a "natural loner" though he was wise, kind & cared deeply for others. If the person is productive and seems happy, i wouldn't worry; if the person is withdrawing from others for the first time, i would be extremely concerned and gently encourage them to talk about it.