However, injuries limited Nielsen as he only appeared in two league matches for New York in 2010. Despite his injury setbacks it was decided that Nielsen would remain in New York for the 2011 season. His injuries continued throughout the entire 2011 MLS season. Nielsen's contract with Red Bull Salzburg - and his associated loan to New York Red Bulls - expired on 31 December 2011. He trained with the club as a trialist during 2012 pre-season camp but was not offered a contract. Nielsen has represented Denmark at every youth level from the Under-16 to the Under-21 side. He has played a total 49 youth internationals, beginning with his October 2002 debut for the Under-16s. He represented the Denmark national under-21 football team in nine games from June 2007 to October 2008.