In a trial  for World Cup selection in 1971, Mullins suffered a broken jaw and again, in 1973 when he was 'king hit' in a game against Manly-Warringah costing him any chance of being selected to the 1973 Kangaroo tour.
Mullins' World Cup selection prospects were hindered by two serious injuries: a broken jaw in 1971 and a severe blow to the head in 1973 during a game against Manly-Warringah.