Providing disability-related leave for an employee is something that employers need to be very careful about. If the leave does not cause undue hardship for the employer, then the Americans With Disabilities Act (ADA) states that you generally have to grant the leave; however, not for an unlimited period of time. If you do not grant the leave even though it would not cause undue hardship, you could be sued.
Factors That Determine Hardship
Workflow impact is often the most critical issue, along with the financial resources of the company. If the employee performs duties that no one else at the company can do, and you can't cover for the position with a temporary hire, then an absence could create a problem. This does not automatically mean that the leave would cause undue hardship, though. For example, if the employee were not disabled and merely had the flu, and he or she wanted a day off to deal with being sick, you'd likely find a way to cover for that employee on that day. So a short leave could still be possible.
Then you'd have to look at the duration of the leave. Again, a short leave of a couple of days would be like letting the employee stay home due to a cold or flu -- you'd be able to cover that, so leave for a disability-related reason should not cause any more hardship for your company than leave for a typical short-term illness.
But if the employee is requesting a very long leave, like multiple weeks or months, then the workflow impact could be severe. If no one else can do that employee's job, and it's not possible to train someone else for the position in the time you have before the employee would need to go on leave, that could be a situation in which you're looking at undue hardship. Basically, if you can't get someone else into the position, not even a temp, and that employee's absence for the requested amount of time would severely hurt your company's operations, that's a major hardship for the company.
It's important to note that the decision to call a leave request unduly difficult for the company should not be done quickly. Employers should consult lawyers familiar with the ADA to ensure they (the employers) have not overlooked something.
Intermittent Leave May Work Out
It's possible that the employee is requesting significant leave but on an intermittent schedule. Missing every Monday and Tuesday for several months could be inconvenient, for sure, but if the employee is still going to be at work for three other days each week, that might not have as severe an impact on you as you might think.
The flexibility and predictability of the leave can also be of importance. If the employee needs a day off every week for physical therapy, but that day can be scheduled at the beginning of each week, that is a much easier situation to work with. The same goes for whether you can tell what leave the employee will need. For example, one day off each week can be scheduled. But multiple days possibly needed each week -- with the employee not knowing until that morning if he or she would need the day off -- would be very difficult for a lot of companies to accommodate.
Again, it's crucial that you consult a lawyer. As inconvenient as the leave might be, it is much better for everyone involved if you can make it work.