In football terminology, a 'donkey' is used as a derogatory term for a player who is slow, clumsy, and lacks creativity or technical skill. This term is particularly used in British football culture. Pony, slug, and monkey are not established football slang terms with this specific meaning.
In sports slang, calling a player a "donkey" is a common derogatory way to describe someone who is clumsy, slow, or lacks skill and imagination on the field. It's a widely used insult in football/rugby commentary and fan culture. The other animals listed (pony, slug, monkey) aren't established slang terms for this in the same way.