Requisition - Mandatory to select at least one approver

Hi Experts,

i have a simple requirement in Purchase Requisition but not too sure how to set this up. Appreciate if you can guide me in setting this up. Thanks in advance.

1) Requester will create a non-catalog item.

2) Before clicking on submit, the system should check if he/she has selected at least 1 approver from the system, if not selected, the system will stop the user from submitting the requisition. The approver can be anyone from the system. It is not required to be employee supervisor relationship.

Please provide some guidance. Thanks.