Dear Sruthi,
When you raise any question on leave or other conditions of service of employees, it is always better to mention the type of establishment to which the question relates.
Since the question relates to casual leave and sick leave, I presume yours is an establishment coming under the State Shops and Establishments Act.
When an employee joins the establishment in the middle of the year, both types of leave would be applicable to him on a proportionate basis only during the rest of the year.
Strictly speaking, the period of probation does not curtail any employment benefits like leave. However, the general industry practice is that probationers would be allowed to avail such leave depending on the length of service they have rendered so far only.