De Sa began his football career in the youth of SV Argon, from where he transferred to the youth squad of Ajax in 2002. He made his debut for the senior squad in a KNVB Cup match on 21 September 2011 against VV Noordwijk, replacing Aras Özbiliz and scoring his first goal in the 61st minute in a 3–1 away win for the Amsterdam side. Although he was included on a few squad lineups for league matches in the 2011–12 Eredivisie season, he didn't make any appearances. Playing for Jong Ajax instead, it wasn't until the following season on 20 October 2012, that De Sa would come into action for the first team in a league match, making his Eredivisie debut in a game against Heracles Almelo, coming on in the 77th minute for Tobias Sana in the 3–3 away draw. His teammate Viktor Fischer made his league debut for the first team in the same match as well.
Starting the 2013–14 season with the reserves team Jong Ajax who had recently been promoted to the Dutch Eerste Divisie, De Sa made his first appearance of the season on 5 August 2013, starting on the right wing in the home match against Telstar, before being substituted off in the 76th minute for Marvin Höner in the 2–0 win at home, marking the reserves teams debut in the second tier of professional football in the Netherlands. He scored his first goal of the season for Jong Ajax on 26 August 2013 scoring the opener in the 1–1 draw at home against FC Emmen.
On 28 August 2013 he was called up to play for the first team in the Eredivisie home match against Go Ahead Eagles where he made his first appearance in the starting line up for the first team. Ajax won the match 6–0, with De Sa scoring the second goal for Ajax only two minutes after the first goal was put in its own net by one of Go Ahead Eagles defenders. Within 5 minutes Ajax scored two more goals to increase the lead by four, with De Sa assisting Kolbeinn Sigþórsson on his first of the two scored with a cross from the right side of the box. De Sa was then substituted off in the 69th minute of the match for Lucas Andersen. The following match saw De Sa starting on the right wing again in what would be his continental debut for the first team in the 2013–14 UEFA Champions League group stage match against A.C. Milan on 1 October 2013. The match ended in a 1–1 draw, with Lesley playing the first 64 minutes before being substituted once more for Lucas Andersen in the home match.
De Sa spent the 2014–15 season on loan at Go Ahead Eagles, playing 16 matches and scoring once.
On 22 June 2015, it was announced that De Sa was being sent on loan to Willem II together with Ruben Ligeon and Richairo Živković.
On 27 November 2007, De Sa made his international debut for the Netherlands at youth level playing for the Netherlands U-15 squad in a friendly match against Slovakia U-15. He scored his first international goal for Netherlands U15 two days later in another friendly match against Slovakia U-15 on 29 November 2007. That season De Sa went on two appear in three more friendly fixtures for Netherlands U-15. One against Belgium U-15, and two matches against Switzerland U-15. On 28 October 2008 he made his debut for the Netherlands U-16 in the 10th edition of the Tournoi de Val-de-Marne '08 in Paris, France against Italy U-16. After his second appearance, a 1–0 away victory over the host nation France U-16, he then scored his first goal for the under-16 team in a match against Uruguay U-16 in the same tournament. He later appeared in two more friendly matches for Netherlands U-16 against both Ukraine U-16 and ireland U-16.
De Sa made his debut for the Netherlands U-17 on 22 September 2009 in a friendly match against France U-17. He played a significant role for the under-17 teams 2010 UEFA European Under-17 Football Championship campaign, making a total of six appearances, while also competing in the La Manga Cup in Murcia, Spain where he scored his first goal against Denmark U-17 in the 2–1 loss.
On 27 November 2010, he made his debut for the under-18 team against Romania U-18, making two further appearances for the Netherlands U-18 that season. On 19 May 2011 he debuted for the Netherlands U-19 in a 2011 UEFA European Under-19 Championship qualification match against Israel U-19, making a total of six appearances in the Dutch U-19 qualifying campaign, also appearing in three friendly matches for the under-19 team that season.As of 2015-12-30
1 Includes UEFA Champions League and UEFA Europa League matches.
2 Includes Johan Cruijff Shield and Play-off matches.Reserves performance
Statistics accurate as of last match played on 27 April 2014.