Upon arrival at Hamburger SV, Jung was immediately sent down to the second team, Hamburger SV II. On 26 July 2014, Gideon made his debut for the side in a 4–0 rout of Goslarer SC 08. On 26 October 2014, Gideon scored 1 of 10 goals for the team during a 10–0 rout of FT Braunschweig. During the 2014–15 season, Gideon appeared 23 times for Hamburger SV II, but wasn't able to make his debut for Hamburger SV.
Having been called up to Hamburger SV, Jung started the 2015–16 on the first team, making his debut on Matchday 1 versus FC Bayern Munich.