Fernandez said Oudin, 19, and Mattek-Sands, 25, will be on the court when the United States takes on defending champion Italy next week in San Diego.
Also on the squad will be 18-year-old Coco Vandeweghe and 34-year-old doubles veteran Liezel Huber.
Team USA will be playing without the formidable Venus and Serena Williams, each of whom pulled out of the competition due to injuries.
The Americans haven't won the Fed Cup since 2000 despite 17 all-time championships. They lost to the Italians in last year's finale, 4-0, in Reggio Calabria, Italy -- the first time Team USA had fallen to the Italians in 10 all-time matches.
Italy, meanwhile, is seeking its third Fed Cup championship.