Discount grocery chain Aldi is expected to unveil on Monday plans to invest $5 billion to open nearly 900 stores and remodel hundreds more in the U.S.

The expansion, over the next five years, puts the German grocer on track to becoming the third-largest food retailer in the U.S. by store count, behind the larger Wal-Mart Stores Inc. and Kroger Co., and a growing threat to traditional food retailers.