This warning has been raised because this index is hypothetical. This means that the index is maintained by SQL Server, but is never used for queries. Hypothetical indexes are generated by the Index Tuning Wizard and Database Tuning Advisor, and although they should be deleted once the tools have finished, there may be cases when an error has caused the index to be left in place. Unless either of the tools are being used right now, hypothetical indexes should be dropped, as they serve no benefit.
Drop the hypothetical index
Any suggestion from Aireforge should be thoroughly tested before being implemented into production.