Australia's Nick Kyrgios returns the ball to Czech Republic's Tomas Berdych during the ATP Marseille Open 13 semi-final tennis match in Marseille on February 20, 2016. / AFP / BERTRAND LANGLOIS (Photo credit should read BERTRAND LANGLOIS/AFP/Getty Images)

Doubt over the availability of Nick Kygrios for Australia's Davis Cup tie with the USA have intensified after the 20-year-old did not train on Tuesday.

The team, including Bernard Tomic who is also under an injury cloud, trained at Kooyong this afternoon, however Kyrgios was no where to be seen.

The youngster withdrew from his semifinal clash wit Stan Wawrinka in Dubai last week due to a back injury.

NewCorp has reported that Kygrios will not attend the official dinner or pre-match media duties so he can remain in Canberra until Wednesday to receive treatment on his back.