The 24-year-old attacking midfielder has made eight Premiership appearances [five starts] since his off-season switch from National First Division outfit Mbombela United.
“He has been doing well at training. It was his eighth game in the Absa Premiership,” Johnson told his club's website following a 1-0 loss to Cape Town City just before the festive break.
“He has done well so far, but I think he still needs to grow as a player.
“Siyethemba has a lot of potential but he needs to hold the ball better.
“He also needs to read the game a little bit better. I think he will improve.”
Usuthu, in 12th place on the standings with 15 points from 13 games, will resume their campaign against mid-table Chippa United at King Zwelithini Stadium on January 7.