Schooled primarily as a centre back, Mancienne can also play as a defensive midfielder as well as both fullback positions as he showed during appearances for Chelsea, and multiple loan spells at Wolverhampton Wanderers.

[3] After gaining playing time with spells on loan at Championship sides Queens Park Rangers and Wolverhampton Wanderers, respectively (see below), he finally made his Chelsea debut on 14 February 2009, starting an FA Cup tie at Watford.

[4] He made his European debut appearance 11 days later as a late substitute in a UEFA Champions League knock-out tie against Juventus, which ended 1–0 to Chelsea.

[6] Mancienne gained his first taste of league football in a loan spell at Queens Park Rangers in late 2006, when he joined them for the remainder of the 2006–07 campaign.

[9] His performances during this period caused Wolves to extend his loan by a further month,[10] however, the paperwork on the extension was never completed, and he was recalled by his parent club.

[13] He suffered a patella tendon injury in December that ruled him out for three months,[14] before he returned to the side for the club's final six games, as they narrowly avoided the drop.

On 31 May 2011, Mancienne signed a four-year deal at German Bundesliga club Hamburger SV for a fee in the region of £1.752 million.

He was reunited with former Chelsea sporting director Frank Arnesen, officially moving on 1 July 2011, when the transfer window opened.

On 16 July 2014, Mancienne joined Nottingham Forest on a three-year deal, reuniting with his England U21 manager Stuart Pearce.

[29] Having missed the opening day of the 2022–23 season, manager Jimmy Floyd Hasselbaink confirmed that he would be out injured for three months with a knee injury.

[33] On 15 November 2008, Fabio Capello surprisingly named him in the England squad to play an international friendly match against Germany in Berlin.