McBreen is one of the team's quota of four foreign players, the other three are goalkeeper Cristian Mora, centre-half Bojan Malisic and midfield stopper Sean Tse Ka-keung.
South China coach Mario Gomez said: "McBreen is the type of striker we are looking for and although he just joined us for a short period of time, there is a month to go before the regional tournament starts and we are confident he can improve his form as required."
McBreen might make his debut as soon as Sunday when South China takes on Pegasus.
Gomez added: "The team is changing and progressing. We will have a fresh look against Pegasus."
Captain Chan Wai-ho added: "We need a good performance against Pegasus if we want to keep our title hopes alive as there is no room for dropping points. The team has been strengthened with the newcomers and the spirit is high. It's time for us to prove it on the field.