Index of table '&1' may be able to be deleted

What causes this issue?

The index for the table is no longer needed. It can thus most likely be
deleted. However, a where-used list will be created beforehand and only
when this shows that no other InfoCube needs this index will it be
deleted.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.