Gillingham assistant boss Ian Hendon has left to take up a development team coach role at West Ham United.
Hendon told BBC Radio Kent: "Every coach, player, manager and probably chairman wants to move on to bigger football clubs and I'm no different.
"To go to a place like West Ham and work with the talented players they have got there is exciting.
Hendon, 39, played for Tottenham, Barnet and Leyton Orient and had spells managing Barnet and Dover Athletic.
Manager Andy Hessenthaler told the club website: "We're disappointed because he worked his socks off for this club.
"But, as a good friend of his, I appreciate that it is something he wanted to do."
Hessenthaler has said that finding a replacement is a top priority.
"There is a void here and I am looking to bring somebody in. I'll sit down with the chairman to see which way we go with that.
"I like doing the coaching. However, if you look around the country and speak to other managers, you see they have their coaches but then they put their mark on sessions leading up to the game.
"I don't know whether we'll have another assistant manager. It would more likely be a coach but it's doubtful we will have anybody in for the weekend."