I am writing a short Sci-Fi story centered entirely on the man vs. beast narrative where the protagonist attempts to escape an unstoppable, bloodthirsty creature for roughly 15 pages. From the first word to the last, there is action galore with tight, bare-bones descriptions of movements and surroundings to let the reader live the fast-paced scenes I intended to create.
Upon re-reading my initial drafts, I realized that I never explicitly motivated the protagonist's escape from the monster. In my mind, a reader would naturally root for him given that he is human and the inhuman monster trying to eat him would be perceived as bad. I know it isn't difficult to motivate his escape, perhaps with subtle references to loved ones he is attempting to return to, but I am against including such tropes if possible.
My question is, is this good enough? Can I really assume that readers will care about my protagonist simply because he is human at odds with an inhuman creature, or must I explicitly motivate the reasons to root for him?