When Ray Wilkins left Chelsea last November most people probably wondered what all the fuss was about. What did Wilkins, an assistant coach, do anyway? Four months later and Chelsea have gone from being four points clear at the top of the table to fifth in the league. It begs the question: just how influential is the role of an assistant manager?

First off I must confess my ignorance. Before I began thinking about this column I would almost certainly have dismissed the job as a trumped up title, a fancy term for what is essentially just another coach. Among players, assistant managers tend just to be referred to as "coach", they perform day-to-day duties but do not have the same authority as a manager. Moreover, to the outside world they are almost invisible.

Inside the training ground, however, they are omnipresent. Managers and their assistants are like two peas in a pod. When you see Harry Redknapp arriving at the Tottenham training ground for work he's always with Kevin Bond. They share a lift up from Bournemouth each day – Bondy in the driving seat, Harry next to him in the front. They go back years and are friends as much as colleagues – which is a worrying requirement for me as a wannabe manager because I don't really have any friends. Where will I find my assistant? My future managerial career could be doomed already.

Assistants play a vital role in getting a manager through the aftermath of a defeat. Dropping three points is an agony that – arguably – a manager feels harder than anyone else. As the person responsible a manager will inevitably doubt his tactics. It is the assistant's job to keep the manager on course. Perhaps that is where the friendship comes in, a strong emotional bond in what might otherwise be a very isolating job.

But simply being friends isn't enough. An assistant's role is a complex and challenging one. He's got to be the manager's right-hand man, and yet he's got to be the players' trusted confidante. When I asked the question on the team bus at Bristol City last week, the players all agreed: the assistant's role is to form the bridge between the team and the manager.

Over the years myself and various team-mates must have spent hours having a moan to the assistant manager. I recall players coming up to me afterwards, worrying whether they had said too much, but you grow to trust an assistant. His job is to listen, allow the players to get things off their chests – sometimes they even agree with the complaints – but never to grass the players up to the manager.

For players the roles are clear and distinct: a manager makes all the tough decisions, hiring, firing and team selection. An assistant manager tends to do anything that the gaffer doesn't feel comfortable with – whether that's coaching work on the field or paperwork in the office. When Harry was at Portsmouth, with Joe Jordan as his assistant, it was Joe who took every single training session while Harry stayed in the office. But when it came to meetings and talking to the players, that was very much Harry's job.

In my experience an assistant tends to be closer to the players – not only because of their job description, but in part because of their career as a footballer. Assistants tend to be ex pros who performed at the highest levels – often in contrast to the manager – for example Pat Rice and Arsène Wenger at Arsenal, Jordan and Redknapp, or the former partnership of José Mourinho and Steve Clarke at Chelsea. The assistant is the archetypal footballer's footballer, someone to look up to, who's done it all before. He is a man who can relate to the team, who can play good cop to the manager's bad cop, and smooth out any disagreements. On a Monday morning, when there are a bunch of aggrieved players on the training pitch, an assistant's job is to keep everybody happy and be compassionate.

As close as he is to the manager an assistant can't be a yes man – he would never get any respect from the players. However, if he was to publicly disagree with the manager it would cause all sorts of ructions. I've only ever once seen an assistant have a row with the manager in front of the team. As soon as we witnessed that going on we knew the whole management structure was in trouble.

Some assistants have had a fling at management and it hasn't quite worked out. Perhaps they didn't get along with the intense media scrutiny, or perhaps they weren't good at making the unpopular decisions. But with the amount of experience they accumulate in their role, it does make me wonder why more assistant managers don't step up to the job of full‑time managers?

Perhaps it is, in part, down to the perceived wisdom that to be a manager you don't actually need to have your coaching badges – except for in European competition. I found this out the other day and was genuinely shocked. I'm working my way through the badges – I think they're very important. Even if I then decide to delegate the coaching side of things to an assistant, it would make sense if I had some idea of what they might be up to on the training pitch. Once I've got my badges sorted I'll just need to find a friend …

David James has donated his fee for this column to charity