Sorry - Update statistics is not required for Index Rebuild, automatically it will be updated. Please refer the below link. I have pasted the specific content below:
After Maintenance Operations
Consider updating statistics after performing maintenance procedures that change the distribution of data, such as truncating a table or performing a bulk insert of a large percentage of the rows. This can avoid future delays in query processing while queries wait for automatic statistics updates.
Operations such as rebuilding, defragmenting, or reorganizing an index do not change the distribution of data. Therefore, you do not need to update statistics after performing ALTER INDEX REBUILD, DBCC REINDEX, DBCC INDEXDEFRAG, or ALTER INDEX REORGANIZE operations. The query optimizer updates statistics when you rebuild an index on a table or view with ALTER INDEX REBUILD or DBCC DBREINDEX, however; this statistics update is a byproduct of re-creating the index. The query optimizer does not update statistics after DBCC INDEXDEFRAG or ALTER INDEX REORGANIZE operations.