Lieutenant General Fonseka returned to the capital Colombo Tuesday after undergoing specialised treatment in Singapore for more than a month, Samarasinghe said.
"He has just started work," Samarasinghe added. "The general is quite all right now.
Fonseka was wounded in an April 25 suicide bomb attack inside the tightly-guarded army headquarters in the capital.
The attack, which killed 11 people, was carried out by a woman pretending to be pregnant.
The army's number three officer, Major General Parami Kulatunga, was killed in a suicide bomb attack in June.
The government has blamed the rebel Liberation Tigers of Tamil Eelam, which has waged a separatist insurgency since 1972, for both attacks.