Van der Merwe suffered the setback while in pre-season training and has subsequently been ruled out until 15 April after undergoing surgery .
Van der Merwe was absent for much of the 2014 season with a knee injury .
Van der Merwe , who was absent for much of the 2014 season with a knee injury , suffered the setback while in pre-season training and has subsequently been ruled out until 15 April after undergoing surgery .