SpotTheCat
Herding cats
It still would be good to start the same way. a fear of being leashed will turn into a fear of the leash because they will pick up on the pattern of the leash being picked up= leash being put on. And the better a reward history he has with the leash the easier it will be to put it on himThose are very good suggestions. At this point I don't know if he is afraid of the leash itself or of just being leashed. I will have to ask the foster for more details.
Definitely get more details I wouldn't be surprised if he is scared of more then just the leash!