Williams aggravated an abdominal strain at Wimbledon and Seles is bothered by a foot injury.
"Fans around the world watched Venus valiantly compete while injured at Wimbledon and we understand her need to recuperate," said Fed Cup captain Billie Jean King. "Monica has been a stalwart contributor to the U.S. Fed Cup effort, but she, too, has been playing hurt and her need to fully heal from a foot injury supersedes this Fed Cup commitment."
King named Chanda Rubin, the world's eighth-ranked player, and Alexandra Stevenson as the replacements. They join Meghann Shaughnessy and Lisa Raymond on the U.S. team that will face Italy in the Fed Cup quarterfinal July 19-20 in Washington.