Sydney: Australia's top-ranked player Nick Kyrgios Thursday said he was withdrawing from next week's Davis Cup World Group showdown against the Czech Republic with a back problem.

Kyrgios was to have joined Bernard Tomic as one of the likely singles players for Australia, with veteran Lleyton Hewitt and Sam Groth completing the line-up under new captain Wally Masur.

"I am totally gutted to have to pull out but the medical advice is that my back is not ready to handle the workload required for a Davis Cup tie," he said in a statement. "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 first-round tie, in Ostrava from March 6-8, will see Australia take on a Czech team without stars Tomas Berdych and Radek Stepanek. Kyrgios, 19, also sat out last month's Hopman Cup with back trouble and he has not played since he reached the Australian Open quarter-finals.

Masur said the 19-year-old Kyrgios had been "positive and desperate to get across the line" but that he needed to have a solid recovery. "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, who had already been due to travel with the squad, was likely to be Kyrgios' replacement.