Nkosi joined Cosmos on loan from Orlando Pirates in August until the end of the 2018/2019 season.
Sono revealed that Nkosi was struggling with fitness and needs to improve if he is ever to get a place in the starting line-up.
Nkosi has played only three games and scored one goal since joining Ezenkosi in August.
The South African football legend complained about the lack of quality in his National First Division club.
Sono says he still hopes to gain promotion into the Absa Premiership.
“We are focused on improving our position on the log. We do not have that luxury to give players individual treatment. Players must work hard in training and we will take it from there,” Sono was quoted by SowetanLIVE.