Australian Open semi-finalist Sloane Stephens was replaced on the US Fed Cup team by Melanie Oudin on Sunday for the Americans' first-round tie next week at Italy.
Teen star Stephens, ranked a career-high 17th in the world and 10-3 on the season, said she suffered an abdominal strain during her Australian Open run.
"I played a lot more matches than I expected in four straight weeks in Australia and need to be careful not to let this ab injury sideline me for a long time," Stephens said.
Oudin, 21, joins Fed Cup newcomers Varvara Lepchenko and Jamie Hampton and doubles veteran Liezel Huber in facing the Italians on clay at Rimini for a US squad that has won a record 17 Fed Cup titles, but none since 2000.
"Melanie is such a team player to answer the call at the 11th hour," US Fed Cup captain Mary Joe Fernandez said. "We were excited for Sloane to make her Fed Cup singles debut, but that will have to wait for another day."
Oudin helped the Americans reach the 2009 and 2010 Fed Cup finals, where they lost each time to Italy. She is 5-8 in Fed Cup ties. Oudin, ranked 85th, won her first WTA singles title last year at Birmingham.