United have been left stunned by Agutter's decision to leave as they make another bid to get out of the Isthmian south-east decision.
Agutter, who led United to the top of the table in each of the unfinished 19-20 and 20-21 seasons, released a statement on Monday morning thanking everyone who had made his four years at The Pilot Field enjoyable - saying the job had given him his best days in football.
He said: "Firstly I'd like to place on record a big thank you to Dean and Ben White for giving me the opportunity to join the club back in 2017, both have been ever-present and continue to drive a thriving academy that gives Hastings United the strongest of foundations from which to move forward.
"Secondly I'd like to acknowledge all the directors, staff and all those behind the scenes that I've been lucky enough to work with during my time at Hastings United, most notably Daren, Peter, Billy, Pat and former director Dave Nessling, all have given me great support and backing and all have trusted me to manage what is a proper sleeping giant of a football club, a privilege I'll be eternally greateful for.
"I'll always miss the support behind the goal and I'll sometimes miss the main-stand support. George, Podcast Chris, Simon Stoddart, Rob, Joe, John Wills, Leon, Sandy, Steve and Harry and so many more - genuinely thank you for being the 12th man.
"A final and most special thank you to all the people I've had the absolute pleasure of sharing the dressing room with over the best part of the past five years, the 18s, 19s, 23s and first team. It's been over 400 games and many more training sessions that have given me my best days in football to date, so many special memories with so many great people that I'll look back on with nothing but pride and happiness.
"I now look forward to the next challenge wherever that may be while wishing Hastings United the very best of luck for the future. COYUs!"
As reported earlier, assistant manager Andrew Brown will take over managerial duties and will lead the team tomorrow (Tues) night against Whitstable Town at the Pilot Field.