grether played his first ever international game for the switzerland u-18 team on the day before his 18th birthday. on 19 may 2010 the swiss team beat ukraine u-18 2–0. grether made his debut for the switzerland u-19 team in the 1–1 draw with czech republic u-19 on 4 september 2010. he played his debut for the switzerland u-20 team in the 3–2 win against the italian u-20 on 31 august 2011.