In July 2011, Warner was included in the Western Province side that participated at the premier high school rugby union competition in South Africa, the Under-18 Craven Week tournament held in Kimberley.
However, he had limited playing time for the Blue Bulls U21 at age-group level – in 2012, he was named on the bench on one occasion during the Under-21 Provincial Championship, but failed to appear, and in 2013, he made just one start and two appearances off the bench, contributing a try in their 37–10 victory over the Leopards U21s in Potchefstroom.
[5] Less than two weeks after his final Vartisy Cup match, Warner also made his first class debut.
He started their Round Five match against Namibian side Welwitschias in Windhoek and helped the Blue Bulls to a 44–0 victory.
Warner was included in the Blue Bulls' senior squad for the 2015 Currie Cup Premier Division and was named as the scrum-half replacement for their Round Four match against Griquas in Kimberley.