Billing Locums without a signed agreement from provider who left

We have a provider who unexpectedly left the medical group. We have hired a locum tenen physician. However, we do not have a signed agreement from the provider who left that states we can bill any work the locum does under the absent provider's NPI.

We're at a loss as to how to proceed. Please advise.

Billing Locums without a signed agreement from provider who left