Australia number one Nick Kyrgios has withdrawn from next week's Davis Cup World Group tie against the Czech Republic because of a back problem.
The 19-year-old also missed the Hopman Cup with back trouble and has not played since losing to Andy Murray in the Australian Open last month.
"I'm totally gutted but medical advice is that my back is not ready," he said.
The Czechs are without Tomas Berdych and Radek Stepanek for the first-round tie in Ostrava from 6-8 March.
Kyrgios was expected to have joined Bernard Tomic as one of the singles players for Australia, with 34-year-old Lleyton Hewitt and Sam Groth completing the line-up under new captain Wally Masur.
"I have been doing everything possible to get it right and I had convinced myself I could handle it, but the doctors tell me the risk is just too great. They say this simply cannot be rushed," the teenager added.
"I really feel for Nick because I know how much he has put into this and how keen he was to play for his country again," Masur said.
Tennis Australia said emerging youngster Thanasi Kokkinakis, 18, who had already been due to travel with the squad, is the likely replacement.