"Gareth broke down in training last Sunday and a scan has revealed a tear to his left calf," said Wales Team Physio Mark Davies.
"He will not be able to run for at least 10 days, ruling him out of preparations for both tests and led to the decision to send him home."
Meanwhile, Dragons back row and former international Captain and British Lion Colin Charvis has been passed fit with a clean bill of health, although wing Aled Brew is not being considered for the first test.
"Colin was put through his paces on arrival in Australia on Monday to test a bone bruise he sustained to his knee," added Davies.
"He has come through the fitness test and has benefited from sitting out on the Dragons game last week leading to him being made available for selection for the first test.
"Aled will not be considered for the first game after carrying a ligament injury to his knee for the last three weeks, but he is making progress and is fully expected to be ready and available for the second test."
Mefin DAVIES (GLOUCESTER RUGBY)
DoB: 02.09.72. 5'10". 15st 0lbs
International record: 37 caps (W 17, L 19, D 1; 10 pts - 2T)
Steve JONES (NEWPORT GWENT DRAGONS)
DoB: 20.04.77. 5'10". 15st 0lbs
International record: 5 caps (W 3, L 2)