Depends on the what caused the leave. I live in the US and my job has short term disability. It pays 70% of my pay for any absence over 14 days. I can also use vacation time to make up the difference in pay.

I have seen medical leave covered by workman's comp. A guy I worked with got so stressed from the job he had a breakdown and needed a leave of absence. The shrink also determined that the job was responsible for the stress/breakdown so was covered under worker's comp. So even though he hadn't paid for the STD (short term disability) insurance he still got paid.