I googled and now wish I hadn't!
Although NHS and a few other sites advise that using the oral antifungal terbinafine doesn't affect (particularly male) fertility, there's some scary reddit posts, a single case study, and I think some mice studies which show DNA fragmentation of sperm.
I'm already late 30s and don't want to wait until my DH's long course of terbinafine is over :(