Of German heritage, Neustädter played for Germany at various youth levels, then being capped twice by the Germany national team in 2012 and 2013. He switched allegiance to Russia in 2016.[2] Apart from Germany and Russia, Neustädter was also eligible for Kazakhstan, Kyrgyzstan, and Ukraine.
Neustädter has often played as a defensive midfielder and centre back.[3] While the former is his preferred position, he mostly played as the latter during his stint at Schalke.[4]
At the end of the 2011–12 season, Neustädter left Mönchengladbach and joined Schalke 04 on a free transfer, signing a four-year contract running until 30 June 2016.[11]
In July 2016, after turning down a new contract at Schalke, Neustädter signed a three-year deal at Fenerbahçe of Turkey.[12]
On 9 August 2019, he signed a one-year contract with Russian club Dynamo Moscow.[13] On 15 October 2020, after the first 10 games of the 2020–21 Russian Premier League were played, he returned to Dynamo until the end of the season.[14]
The Football Federation of Ukraine has expressed interest in calling up Neustädter for their national team. Neustädter, who was born in Ukrainian SSR, has indicated that he would be likely to accept a call-up if asked. He would first require to obtain a Ukrainian passport in order to be eligible for national team duties.[17]
On 9 November 2012, Neustädter was called up for the Germany squad to face the Netherlands in a friendly match five days later.[18][19] He made his debut for Germany in this match as a late substitute for Schalke team-mate Lewis Holtby.
In January 2016, Neustädter met with members of the Russian Football Union in order to be able to possibly play for the Russia national team in the future.[20] On 21 May 2016, he was called up to represent Russia at UEFA Euro 2016.[21] On 1 June 2016, Neustädter made his debut for Russia, in a 2–1 friendly loss to the Czech Republic, as a 64th-minute substitute.[22] He started Russia's first two games during the final tournament in France, where Russia failed to proceed through the group stage.[12]
On 11 May 2018, he was included in Russia's extended 2018 FIFA World Cup squad.[23] He was, however, not included in the final World Cup squad.[24]