Paris - Serena and Venus Williams have opted out of the United States team to face France in the Fed Cup semi-finals, the US Tennis Association (USTA) announced on Wednesday.
The sisters played in the first-round win over the Netherlands in North Carolina in February, but have decided not to make the trip to France for the semi-final at Aix-en-Provence on April 21-22.
Serena, a 23-time major singles champion, marked her return to action in the first-round tie after 13 months away from the sport to give birth to her first daughter and get married.
She lost the 'dead' doubles rubber with Venus in that match against the Dutch.
Venus, meanwhile, won both her singles for the defending champions.
Serena's return to the WTA tour has not gone smoothly with a third-round defeat to Venus at Indian Wells followed by a first-round exit at the hands of Naomi Osaka in Miami.
With both sisters absent, US captain Kathy Rinaldi has instead called up US Open champion and world No 9 Sloane Stephens, world No 13 Madison Keys, 16th-ranked CoCo Vandeweghe and former top-ranked doubles player, Bethanie Mattek-Sands.
France will feature world No 19 Kristina Mladenovic, Pauline Parmentier, ranked 120th, and No 195 Amandine Hesse - the same trio which defeated Belgium 3-2 in the first round.
The other semi-final sees Germany host 10-time Fed Cup champions Czech Republic in Stuttgart.
Julia Goerges and former world No 1 Angelique Kerber, the 2016 Australian and US Open champion, spearhead the German challenge.
World No 6 Karolina Pliskova and 10th-ranked two-time Wimbledon champion Petra Kvitova will bear the burden of singles play for the Czechs who have won five of the last seven Fed Cups.