Cyle Brink, Dylan Smith and Robbie Coetzee have been ruled out for the remainder of the season.
The Lions confirmed on Tuesday that they will only return to action in 2019.
Brink was initially included in the Springbok squad for the Rugby Championship, but sustained a knee injury in training in Durban last week.
Meanwhile, scrumhalf Nic Groom will be sidelined until October as he is still nursing the hand fracture he suffered against the Bulls in Super Rugby.
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