Switzerland's No.1 Belinda Bencic has withdrawn due to a back injury from a Fed Cup semifinal against defending champions the Czech Republic next weekend.
The Swiss tennis federation says world No.10 Bencic must rest for at least four weeks.
The 19-year-old carried the injury since playing at Indian Wells last month and lost her first-round match at the Charleston tournament last week.
Switzerland hosts the Czechs next Saturday and Sunday on indoor hard courts at Lucerne.
Swiss Tennis says captain Heinz Guenthardt is yet to decide whether to call up a replacement in a team that includes top-ranked doubles player Martina Hingis.
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The Czechs, winners of four of the past five Fed Cup titles, will also be without their top-ranked player - two-time Wimbledon champion Petra Kvitova.
