The only potential for a human crossbreed would be with a chimpanzee or bonobo since they are our closest relatives. An interesting thing about the dividing line of species, it's not much of a line and is based on genetic isolation. The less contact two family lines have with each other, the more they drift apart, accumulating new material from mutation and losing old genetic material from decay (a trait not maintained will break down through the generations). What should be obvious here is, the dividing line of species only exists laterally in time: that is, between modern crocodiles, modern humans, modern cats, modern gorillas.
Go backwards in time and you get genetic merging instead of drifting, isolation becomes consolidation. Distant cousins have brother and sister as their ancestors and humans become close kindred with other (now extinct) hominids. Go back further and the ancestors of humans and the ancestors of chimps are still dating each other. There is no species line when you travel back through time. Even when just looking at modern species, that line can be fuzzy because the emerging species (like lions and tigers for example) may no longer be brother and sister but are still kissing cousins. If they remain isolated genetically long enough through geographic distribution, their great grandchildren will evetuaaly be too genetically different to hybridize at all. Yes, this can happen to humans too.
Thanks to the modern ability to travel anywhere, genetic lineages that were growing apart are now more likley to mix, thus we have one species of human. But say in the future we colonize other worlds and due to the difficulty of space travel those colonies rarely if ever mix with each other. This would inevitably, over thousands of generations, result in genetic drift and multiple human species, as separate from each other as we are from chimpanzees.