Career
He has played 49 games for various Danish youth team selections, including nine matches for the Denmark national under-21 football team Club
Nielsen began his career in the youth ranks of small Danish clubs Hjorten IF and Herlev IF, before joining the youth ranks of Akademisk Boldklub (Bachelor of Arts) in the second-tier Danish 1st Division. He played 28 first team games and scored two goals as a semi-professional for Bachelor of Arts. He played 23 of 33 games and scored one goal during the 2006-2007 Superliga season, as the club were relegated to the 1st Division.
He played 28 games and scored five goals in the 2008-2009 Superliga, but could not keep the club from being relegated once more.
In his time with Vejle, Nielsen appeared in 99 official matches scoring 20 goals. With his contract expiring in December 2010, he was linked with the Danish clubs OB, Football Club Copenhagen and Football Club Midtjylland in November 2009.
On 1 December 2009, it was announced that he was trialing with Schalke 04. Schalke manager Felix Magath said he could clearly see some perspective in the young winger, but an injury caused him to return to Denmark after a single training session.
On April 14, 2010, Nielsen was loaned out to United States club New York Red Bulls.
The deal was a cooperation between New York Red Bulls and Austrian club Red Bulletin Salzburg, with Nielsen scheduled to ultimately join Red Bulletin Salzburg on 1 January 2011, according to Salzburg official Christoph Freund. As the Austrian transfer window was already closed, a direct buy was not possible for Salzburg, with Nielsen instead moving to New York Red Bulls as the United States transfer window was open until April 15. Salzburg purchased Nielsen in 2010-2011 and loaned him back to New York for the 2011 Master of Library Science season.
Having waited for the approval of his United States. visa application, he was seen to make an instant impact by head coach Hans Backe.
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 Master of Library Science season. Nielsen"s contract with Red Bulletin 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.
International
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.
Club
Vejle BK
Danish 1st Division: 2005-2006, 2007-2008
New York Red Bulls
Eastern Conference regular season: 2010.