There is only one truly invincible opponent a footballer will ever face. Time. It is unmoved by intimidation, contemptuous of mind games, cannot be outwitted by elaborate tactical master plans and is brutally unsympathetic to those it determines to be nearing a career's end.

Liverpool's Jamie Carragher is aware of just how ruthless it can be. He is far from finished at Anfield, but last week at Stamford Bridge he experienced a sobering reminder of his footballing mortality. He was available for an important Liverpool game and was not picked. That had not happened for 11 seasons and could be repeated against Manchester City at Anfield tomorrow.

Several years ago, such decisions might have brought consternation. Today finds Carragher (33) in his deep-thinking role, adapting to unfamiliar but inevitable changes in circumstances and already assessing what lies in store when his No 23 jersey is surely retired with him.

"I am not the future of Liverpool. Daniel Agger, Martin Skrtel and Sebastian Coates are," said Carragher. "But I can still be part of the present for a few more years. It's only one game I've not been selected for, so it's not the end yet.

"Over the last decade, if I had missed a match, I would have gone straight back into the team when available. This time I didn't, and I have to accept it, agree with it and understand it. I was out for a couple of weeks and the lads who came in did really well. I've always said mental strength is important in every player and this is another test of that.

"In the past there were people saying if Steven Gerrard and me weren't playing there was a problem, but now you look at it and say out of the last three games we've won two away from home. That's good for the club. We have to look to the future. I'm sure the manager, (director of football) Damien Comolli and owners are looking at that while wanting to make sure we're doing everything to win from one week to the next. I think I can speak for Stevie, too, when I say we're desperate to help the club win trophies as much as we can, whether we play all the games or not.

"That has always been our aim. I still always want to play the next game, but this club has been great to me and I will never be disrespectful to it or to anyone who is selected ahead of me. That was one of the things Gerard Houllier always said to me. You must respect those that are playing, especially those in your position.

"If I've played nearly 700 games for Liverpool, it means someone else has been on the bench showing respect for me, so I have no problem when it is the other way around. I am at one of the biggest teams in the world, a club which is looking for players in every country. We're not some Mickey Mouse club short of top-class players, so to have been able to go straight back into the team every time for so long has been a great achievement.

"You want to be involved and you're disappointed when you are not, but I am aware my situation is changing over the next few years. Last weekend may have been one of the first signs of that."

Thoughts inevitably drift to what happens once those signs are displayed more frequently. It is widely presumed that Carragher will take the fast track into management, but he is cautious about committing to a coaching career. He says he has learnt from the best and wants to continue doing so before making a decision.

"I have an idea what I would like to do," he says. "You're basically left with two options when you finish; the managerial route or a media job.

Whatever's best for my family and me will determine that. I'm not 100pc certain to become a manager because I won't take any job just to stay in the game and I have done some media work, which I enjoy.

"In my first year after retiring, I will take time out with the family and also try to see how different coaches work. Maybe I will try to see how Pep Guardiola, Jose Mourinho and some of the top Italian coaches work on the training ground. Arsene Wenger, too. I try and analyse everything -- why a manager has made one decision over another. It's not to be critical; it is because I always think about the game after it's been played. Management is getting more difficult because everyone has an opinion now. It used to just be the press, but now it is the public through social networking on Twitter, Facebook and whatever else.

"People need to understand how difficult it is for players to go straight into coaching. Andre Villas-Boas started his coaching badge at 16, so think how far ahead he is of a player just starting that process in his early thirties. It takes a long time to get the qualifications, although you pick up experience and knowledge from playing.

"Stuart Pearce organised it for me to spend time on the FA licence course in Reading last summer and I really enjoyed it and I will definitely do the two-week course needed to pass all my badges."

The FA are keen for Carragher to become one of their elite coaches. It is easy to see why given the broad education he has received at Liverpool, as they have dabbled in varying football philosophies over the past decade.

"We all want to play the Barcelona way, but we can't," he says.

"People are getting too obsessed about copying them. Even when they're in a bit of trouble you see goalkeepers wanting to show what good footballers they are, playing it from the back.

"What did Alex Ferguson say about David de Gea's mistake against Benfica the other night? That he should have kicked the ball into the stand. He is right, but Barcelona have changed how people think about the game.

"I love watching them play, but they had the same philosophy during the days they were struggling to qualify for the Champions League and we were beating them in the Uefa Cup. They just have players that are a lot better at it now.

"When I started, everyone was saying the same about Ajax. They were the blueprint for our academy. Then everyone was talking about Clairefontaine in France. Now it's all about La Maisa. We always want to do what everyone else has already done. It is right to study them, but there is no point copying. What we have to develop is our own identity.

"I read what my friend Xabi Alonso said about tackling being perceived as a quality here, but that's part of our culture. Maybe it mattered more 20 years ago, but you can't just change the culture of a country.

"Every father who watches his son play wants him to be a great footballer, but they are also intent on making sure he is not a coward on the pitch.

"That's the mentality. Wenger explained it very well when he said the English always go to war.

"It's not just about being able to tackle and nothing else, but you want players with the full package. If you can develop the technique, it's competitiveness that can give us an extra edge over other countries.

"Don't give me all this 'it's the fancy dan foreign coaches' who play all the great football, either. Of all the managers I've had at Liverpool, the ones who wanted to play the most football were a fella from Bootle, Roy Evans, and a fella from Glasgow, Kenny Dalglish. I'm not saying the others wanted long-ball football, but they were more tactical and that meant doing anything to win, even if it meant hitting it early to the big man up front, Emile Heskey, who Gerard Houllier bought, or Peter Crouch, signed by Rafa Benitez.

"We would go to Europe, play 10 men behind the ball and get a result and we were very successful playing that way, winning everything but the league title. It's not right to criticise that, either, but it has been like that in this country for a long time.

"Sven-Goran Eriksson and Fabio Capello were the same. It is always about the players you've got. It doesn't matter which way you go, the game of football is there to be won and there are many different ways to do it."

As the passion rises in Carragher's voice, so it becomes clear what a loss he will be to Liverpool and English football if he does not make the transition from the pitch to the technical area.

"Who knows what the future holds?" he asks, the interview ending while Carragher still has much more to offer. Time, as ever, makes subjects of us all. (© Daily Telegraph, London)

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