Cika wannan jumla: A shekarar 2015, an kira Masterson a cikin tawagar 'yan wasan Ireland masu tasowa don gasar zakarun Turai.
Kofin Tbilisi na shekarar 2015. An yi amfani da shi a matsayin mai maye gurbin kyaftin Rhys Ruddock a wasan farko da Emerging Italy, kafin ya fara wasannin da Uruguay da Georgia, a lamba 8 da blindside flanker bi da bi. Masterson ya zira kwallaye a kan Georgia a cikin nasarar da ta tabbatar da taken farko a gasar don ƙungiyar.