This is a stretch, since "getting sick" isn't generally something one controls directly. At most, it could incentivize illness-risking behavior. However, even then, to be an incentive, the benefit of paid leave combined with being sick during that leave would have to be more attractive than being healthy and working, which is not a foregone conclusion.

Instead, lacking distinct sick leave perversely incentivizes getting coworkers sick (in situations that a sickness is contagious and workers are co-located). Rather, it incentivizes the risky behavior, where the risk is borne by everyone else and, by extension, the employer.