Budget availability check on purchase requisition stage

[bilya2]

Hello dear experts,
I wish to make a credit (budget) check at the purchase requisition stage .
The purpose is to get indication (even a warning message) about the budget availability before the user creates a purchase order.

Any ideas about a way to accomplish the above?

Thank you for your help
bilya

P.S.
Posted this message week ago on the MM forum but no answer there.