David was also part of the England team in the 2002 UEFA European Under-17 Football Championship who reached the semi-final in Denmark and finished in 3rd place.
Mannix is a product of Liverpool Football Club's Academy, and played regularly for the reserves, making over 60 appearances.
Mannix was one of the youngest ever players to play for Liverpool reserves: he was 15 and was moved to train at Melwood with the first team aged 16.
But for his injuries he would be playing regularly for the reserves and making tremendous progress towards being the next Academy player through to the first team squad.
[14] After this incident, Mannix managed to fight his way back into the first team and played in every game for Chester from the end of January.
Mannix managed to score his first professional league goal on 28 February 2009 against Dagenham and Redbridge for Chester with a header into the top right corner.
[15] Mannix made an important start to his career at Vauxhall Motors by scoring the only goal of the game in their 1–0 victory against Newcastle Town to help the side reach the FA Cup first round.