A couple of thoughts come to mind. An "innocent" man, imo, and as alanabit implied, is one who has NOT slept with the woman. One who has, in the pertinent time frame, imo, left himself open to being nailed for support BECAUSE not only did the woman not use contraception, neither did he.
The day should be past when we blame a fertile woman more for getting pregnant than we blame a fertile man for getting her pregnant.