Grimsby's first summer signing was 22 year-old midfielder, Mitch Rose, who had been recently released from Newport County, on a two-year deal. Three days later, they announced the signing of Siriki Dembélé, a midfielder from the Nike Academy, on a one-year deal. They also signed former Port Vale winger, Sam Kelly, on a two-year deal. On 23 June, Grimsby announced their fourth signing, former Leyton Orient and Coventry City defender Nathan Clarke. Five more players were signed before the window closed, most notably former Scotland international Paul Dixon and former Scunthorpe United winger Martyn Woolford. New signing, Nathan Clarke was immediately made captain of the much-changed Grimsby side, following the departure of former captain, Craig Disley. The club only managed one in their first four games of their second season, with a surprise 3–1 victory over Chesterfield. October and November 2017 saw high levels of inconsistency for Grimsby. Attendances dropped as a result, and many fans began to call for manager, Russell Slade, to be sacked. After a brief upturn in form, Grimsby went without a win from mid-December 2017. This caused many fans to again call for the sacking of Russell Slade. Slade was sacked on 11 February 2018 after seeing the team fail to win in 12 league games, with eight losses, he left the team 17th in League Two. Paul Wilkinson took over as caretaker manager following the sacking. During this time, Grimsby faced further defeats against Cambridge United and Exeter City. Michael Jolley was appointed as the new manager on 2 March 2018. Jolley secured Grimsby's safety with 4 wins and 3 draws in his 10 games in charge. On 9 May 2018, it was announced that a total of 12 players would be leaving the club, with Ben Davies and Nathan Clarke two of the more notable departures. Six players were offered new deals, including club stalwart, James McKeown. Two days later, the club announced the departure of assistant manager, Paul Wilkinson, who had been brought in under the tenure of the previous manager, Russell Slade.