Not a fungal problem that I readily recognise. Mallows are usually trouble-free in this respect. I am wondering if the leaf of your hibiscus has been adopted as a nursery for some spider or other visitor. If in doubt, remove the affected leaf and keep if for a while, say, in a glass jar and observe. Otherwise, remove and burn.
This is a rust fungus, most likely Hollyhock Rust (Puccinia malvacearum) which affects many members of the Mallow Family (Malvaceae) including Hibiscus.
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.