Checking up on is an action that implies monitoring, verifying, or investigating someone or something to ensure that they are on track or within acceptable limits. However, there are several antonyms for this phrase, including ignoring, neglecting, avoiding, overlooking, and disregarding. When you ignore someone, you deliberately choose not to pay attention to them. Neglecting means failing to take care of someone or something properly. Avoiding is not dealing with something by choosing to stay away from it altogether, while overlooking implies not noticing something or giving it enough attention. Lastly, disregarding implies ignoring or dismissing something entirely without thought or consideration. Therefore, depending on the context, there can be several antonyms for checking up on.