Wal-Mart Stores Inc on Tuesday named Bill Simon to run its U.S. discount stores, which have struggled with sluggish sales as their core customer continues to be pressured by high unemployment.

Simon, who had been chief operating officer of the unit, replaces Vice Chairman Eduardo Castro-Wright, who was appointed head of the company's Global.com and global sourcing units.

Wal-Mart shares were down 1 percent at $49.12 in premarket electronic trading on Tuesday.

(Reporting by Brad Dorfman, editing by Gerald E. McCormick)