The Bafana Bafana striker joined Cape Town City in September last year, but he failed to play an official match for the club due to off-field issues. He was then released in January.
According to TimesLive, Mosimane asked City chairman John Comitis why they let Rantie go, before he invited him for training.
City had signed the striker to help him revive his career after walking out of Turkish club Gençlerbirliği S.K in 2017.
Comitis earlier confirmed that the striker was released because of personal issues.
City coach Benni McCarthy later expressed his disappointment at not being able to revive his former Orlando Pirates teammate’s career.
For more news your way, download The Citizen’s app for iOS and Android.
Download our app and read this and other great stories on the move. Available for Android and iOS.