Can I be terminated from employment if I’m on medical leave?

What do you mean by "on medical leave? If you are using FMLA leave (your company is covered and you are eligible; you can find the criteria on the U.S. Department of Labor website) you cannot be terminated for being absent while on it; and you cannot be terminated for a medical absence if the employer has agreed to let you take leave, or while you are using earned PTO (like sick or vacation days) to cover your absence. But if you aren't using PTO, FMLA, or an otherwise-employer-approved leave, but are simply out because a doctor, etc. says you should not go to work, you can be terminated: the employer is *not* required to retain employees who miss work without authorization, permission, or using leave guaranteed by law.
The above refers to being terminated due to being on leave. However, more generally, you can be terminated while on medical leave for any reason not connected with the leave or medical condition, which otherwise would be a valid reason for termination. So even while on leave, if the company is resturing or downsizing, you can be terminated; you can also be terminated for poor performance, for insubordination, for breach of policy, etc. Medical leave does not protect you from non-medically related termination.