Revealing the news, he says: "I have decided to retire. I made the decision two weeks ago really, but I have not told anyone except my family.
"It is not one of those situations you take lightly, but I took my time, had a good think about it, spoke to my family, took some holiday, and decided I had had enough."
The Stepney-born midfielder, something of a cult hero with the fans, says he had the opportunity to carry on for a 20th year.
"There were two offers abroad, America and Dubai, and America would have been good for me because I wanted to go there but the family didn't want to move," he says.
"Dubai would have been good financially, and there were a couple of good clubs here, Cardiff and Coventry, that wanted to take me.
"But I thought long and hard about it and decided I wanted to retire."
John, who began his career at Tottenham in 1984, says it would be lovely if the new man wanted to give him a trial so he could complete a decade at West Ham - but he is not holding his breath.
"That would be nice," he admits, "because at the end of the day it is the only club I wanted to play for and having been there so long there is no way I would have retired this year.
"I would have gone another year and done my best, but football happens like that and it is on people's decisions - I accept it, to be honest, I have got no sour grapes.
"Of course I would come back, though, it goes without saying, but at the end of the day one door shuts, another door opens, and you have just got to get on with it.
"I sort of decided that I am not going to play anymore, especially with the travelling up the motorway; I will concentrate on other things."
Speaking candidly about his last year, he adds: "To be totally honest it knocked the stuffing out of me to leave on that note after nine years - it killed me a little bit.
"I think Glenn had obviously made that decision, which he had told me before the end of the season, and I knew about - but it just seemed a shame because it was a big decision for me personally.
"I would have loved to have been there 10 years and got a testimonial. I don't know if the club went along with that decision and all decided together or whether it was a plan from just the manager.
"But it turns out that the manager goes and gets the sack after I don't know how many games, and you just think it might have been a year more that I might have got here.
"The biggest disappointment is not making it to 10 years and looking back I could have gone to QPR, Arsenal were interested in me, as were Bolton going back to my earlier days at the club.
"So it was a decision that a lot of times, three times in fact and other enquiries that I could have pursued, I could have looked at but I always wanted to stay.
"I showed a lot of loyalty but over the last three or four years people forget you because you are not playing as much.
"But I have been a good servant and it is just disappointing that it had to finish that way, getting the elbow, so to speak, after nine years and also getting relegated.
"It was a blow that I didn't start one of those games last year - it was horrible watching.
"I think you train all week and at the end of the day when it is going pear-shaped as it was I think changes there would have been welcome.
"I don't know but I think it was only me and Don Hutchison that didn't get a start all year out of the senior players - I found it a little bit hard to take but that is football.
"I always wanted to finish at West Ham and although it is a little bit disheartening for me the way it ended it was a great time for me with great fans and it is a great club - and hopefully they are going to crack on."
After leaving Spurs for Swindon in 1992 for £80,000, having had loan spells at Nottingham Forest, Ipswich, Brentford, Portsmouth, Cambridge, and Doncaster, he joined the Hammers in 1994 for £900,000.
"It is the best club I have ever played for and I am proud to have played there and at the end of the day it has been good memories," he says.
"I have made some great friends over the years and it is just a shame that they have had to get rid of so many players and you just see it all crumble.
"Once they got rid of us free transfers like me, Winterburn, and Di Canio, those sort of players that were old, to get us off the wage bill, you thought that maybe you were going to keep your younger lot which was good.
"Try and save some dough on wages and try and keep the nucleus together; but in the end it all went pear-shaped and in the end they were selling half the team.
"But to get rid of all of us when we all knew we could easily do a job at that level...it was sad that half the squad, experienced players that had spent their careers in the top flight, and then sell your younger players.
"All of a sudden you are having to buy other players to build it up again.
"But hopefully it will all progress, they will get another manager in, and it will all go from there - I wish them all the best and I sincerely hope they go up this year.
"Hopefully they will get someone in quickly who can get everyone together so it is a settled ship, because at the moment after losing Glenn it is a little bit up in the air."
As for John's immediate plans, he says: "I was always going to take a year off. I have three boys and two of them play football at a good level, so I will keep my eye in there and I am going to take it easy.
"I have got a coaching badge and I play a lot of golf so I am just going to do those sort of things and business-wise I do property and stuff.
"But nothing is ever going to replace playing football so what else can you do?
"At the minute I am not going to do coaching because the jobs I have been offered are academy jobs, and I would miss my boys playing on a Sunday.
"I don't really want to miss their best years so I will watch them for a little while, and obviously I am young enough for the coaching door to always be there.
"I have my UEFA 'B' badge so it wouldn't be a problem getting a job at clubs, though at what level I don't know - but there is always that option.
"The lads who play are 10 and seven and that is probably the best years when they enjoy their football as young kids - so it gives me a bit of pleasure watching them.
"Even the seven year old has had clubs wanting to take him. They are in the Tottenham academy at the minute but the London clubs want to take them on.
"But it is too early and they just need to enjoy it for a little while - but we might see another Moncur in a West Ham shirt one day!"
And so it is that John can muse over some very happy memories at Upton Park, and he adds: "I used to love it at Upton Park whether it was starting or coming on as sub - I used to love the buzz of playing out there.
"There were great times when we avoided relegation in the early days and I played a big part in that and there were cup finals when you are suddenly safe.
"Then it was good to be involved in the turnaround when we got into Europe; I played all those games in the InterToto and things.
"There was a change in the club then from a relegation-struggling club to one that was pushing for Europe.
"I think those crunch games where you came out on top were the best memories."
John worked under three managers at West Ham - Billy Bonds, Harry Redknapp, and Glenn Roeder, and he says: "They were all different in style but all three of them good managers, different types, and all a pleasure to work with, really."
John will be back, though, and says: "I have a lot of mates who are out and out West Ham fans; they used to be on the terraces week in, week out and a few of them do the corporate things there.
"So they have worked all the home games I am going to go to and I am going to enjoy going back to see a few games - Millwall is the first one I will be at."
In the latter days of his career John became a christian, and he explains: "It is a personal thing; all people believe in different things and that is what I believe in.
"Fredi Kanoute was a moslem and it is a case of 'each to their own' but it is a big part of what I believe in."
Some might be surprised, given his 'cheeky' ways on the football field - just ask female official Wendy Toms - but he says: "At the end of the day it is entertainment really and you don't mean any harm to anyone or to upset people.
"I am no saint; I have done things wrong left, right, and centre as everyone knows and I used to get things wrong on the football field, obviously - that is just who you are."
As a great mickey-taker, and given that footballers are rarely religious, he nonetheless didn't find it difficult.
"They can say what they like about me, I am not really worried," he says.
But did it change him as a person?
"I don't really know; you will have to ask my wife that!"
More mellow, perhaps?
"I am, sitting here - because I am not playing football.
"Football is a game of emotions and it hard to control every emotion on the football field; it is something that I couldn't actually do."