Technically, employers are prohibited from discriminating against an employee because he or she is sick. If an employee is treated differently because he or she develops an illness, which might require time off from work, the employer’s actions may constitute unlawful discrimination.
If the employee’s illness is legitimate and supported by medical documentation, an employer should allow such an employee time off (not necessarily paid leave – entitlement to payment depends on the particular circumstances) to recover, and make that employee’s job available on a return or a graduated return to work.
If the illness and absence from work persist for an inordinate and unexpected time period, the issue of “frustration” of contract may arise.
These issues are complex and difficult to assess – experienced legal counsel should be sought in these cases.