Following his public disagreement with manager Tony Humes in February 2015 when substituted in the game against Doncaster Rovers, Sean Clohessy had his contract terminated just one year into his two-year deal, having made 37 appearances for the club and captained the side.

Following him out the exit door was Dominic Smith, who made his one and only first-team appearance in Humes' first game in charge against Walsall in September 2014, following the expiry of his one-year deal.

Okuonghae, who had spent six years with the U's, played 215 games for the club, but a ruptured achilles tendon early in the previous campaign brought a premature end to his season.

[10] Meanwhile, winger Dion Sembie-Ferris, who made his first-team debut against Cardiff City in the FA Cup third round last season, committed his future to the club by signing a new three-year deal.

[16] On 10 June, it was announced that former West Ham United youngster Kieran Bailey had signed a development contract with the club, after he had featured for John McGreal's under-21 squad during the closing stages of the 2014–15 season.

[19] Left-back Ben Gordon was allowed to leave the club on 1 July, having been displaced in the first-team by Matthew Briggs last season and his subsequent arrival on a permanent basis.

[22] Colchester then announced the signing of former Yeovil Town midfielder and captain Joe Edwards on 6 July on a free transfer,[23] joining on a one-year contract with an option of a further year.

[31] The U's suffered their first defeat of pre-season on 25 July when they hosted Leyton Orient at the Community Stadium, losing 3–0 during a game which saw the return of Sam Walker from injury.

[50] A late penalty save from Jamie Jones ensured Colchester held on to their lead and their first win of the season on 15 September as they edged out 3–2 winners against Sheffield United at Brammall Lane.

[55] Ahead of Colchester's final game of the month on 29 September, Callum Harriott was named in the Football League Team of the Week for matchday nine on the back of his run of good form and goal against Swindon the previous weekend.

[58] George Moncur was named as the PFA's Fans Player of the Month for September on 6 October, seeing off competition from fellow finalists Adam Armstrong of Coventry City and Burton Albion's Stuart Beavon.

[65] After struggling to make an impression in the first-team this term, Sammie Szmodics was loaned out to National League club Braintree Town on 30 October in an initial month-long deal.

[71] The newly installed management team immediately recalled Sammie Szmodics from his Braintree Town loan on 27 November ahead of Colchester's trip to Burton Albion.

[73] Chairman Robbie Cowling decided to install a caretaker manager on 2 December in the shape of former U's defender and under-18 coach Wayne Brown, with McGreal assisting while Hall would remain with the club.

Rhys Murphy opened the scoring for Oldham after just five minutes, but a late Chris Porter strike against his former club ensured Colchester could not earn an unwanted record of ten consecutive league defeats.

[84] He made his first signing of the transfer window on 7 January, bringing in Norwich City's reserve goalkeeper Jake Kean on an initial 28-day loan deal.

[3] Kevin Keen made his first permanent signing on 20 January, bringing in former England international defender Nicky Shorey on a deal until the end of the season.

[89] While James Bransgrove became the latest player to join Maldon & Tiptree on loan on 22 January,[90] it was reported that the club had turned down an offer for Alex Gilbey from Championship side Bristol City.

Despite losing Alex Gilbey after 36 minutes having been sent off for a challenge on Southend's Ryan Leonard, Colchester put in a solid defensive display against their county neighbour with only ten men.

[102] With Tom Eastman suspended following his red card at Bury, reinforcements arrived from West Ham on 26 February, with Leo Chambers joining for an initial month-long loan, while Tottenham winger Nathan Oduwa also signed for a month.

Handing a professional debut to Femi Akinwande, Keen's Colchester side fell behind to Wigan on 36-minutes when Yanic Wildschut scored, but four minutes later, Alex Gilbey equalised with a long-range strike.

[108] Another precious win was cruelly stolen from Colchester by Walsall on 19 March at the Bescot Stadium when two goals in the final minutes of the game for the home side consigned the U's to a 2–1 defeat.

[114] Colchester's result against Coventry earned the club the League Managers Association 'Performance of the Week' award, as voted by the panel consisting of LMA chairman Howard Wilkinson, Alex Ferguson, Joe Royle, Dave Bassett and Barry Fry.

[121] Their fate was finally sealed on 23 April when they were beaten 3–0 at home to promotion hopefuls Burton, spelling a return to the fourth tier of English football for the first time in 18-years.

[126] With McGreal's role set to commence following Colchester's game with Rochdale on 8 May, Ball was named as the club's fifth caretaker manager of the season after David Wright was made unavailable for "personal reasons".

[127] Ahead of the final game of the campaign, three development squad players signed new one-year deals with the club, with Charley Edge, Michael O'Donoghue and Chris Regis all agreeing new contracts.

Caretaker manager Steve Ball had named Dillon Barnes in the first-team as goalkeeper, which would have been his professional debut following Elliot Parish's injury the previous weekend.

Bonne was brought off in the final minute of stoppage time, making way for debutant midfielder Jack Curtis to experience his first brief taste of professional football.

[137] Caretaker manager Wayne Brown led his side to victory in his first match in charge thanks to a Callum Harriott goal in the fourth minute of stoppage time to beat the National League outfit 3–2.

[139] After beating Charlton, Colchester were given a home tie against Premier League opposition in the fourth round draw on 11 January 2016, with either Leicester City or Tottenham Hotspur visiting the Community Stadium.