Mmema, who is popularly known as 'Zuma', plays as a defensive midfielder, while Msibi is an offensive midfielder.
City manager Costa Bellos confirmed Papic has called up the pair.
"Yes, it's true those youngsters have been promoted," says Bellos.
"They are already training with the senior team."
The Diski Challenge - which serves as a reserve league to the Absa Premiership - will resume on 17 January, with City up against Mamelodi Sundowns in the quarter-finals of the competition.