It is thought to be no bigger than a pea and it floats around randomly behind John Terry's kneecap. Unfortunately for English football, this tiny piece of debris last night ruled the England captain out of tonight's crucial Euro 2008 qualifier against Russia and set Steve McClaren's preparations into a spin once again.
Of all the times for it to strike, the Terry knee problem picked the cruellest of moments. The 26-year-old had just delivered his most confident and articulate press conference since taking over the captaincy 14 months earlier; afterwards he went out on to the slippery artificial surface of the Luzhniki stadium for England's final pre-match training session. One hour later Terry's knee was locked and McClaren was forced into a sharp rethink of his plans.
For Terry the future is now a simple operation that will probably take place on Friday and will not rule him out for any more than a week. It is no consolation for McClaren, however, who goes into tonight's match without his leader and placing his confidence in Sol Campbell once again. No one doubts the qualities of the 33-year-old but the consensus from the England players last night was that the Luzhniki pitch was an extremely quick surface, which is not ideally suited to the Portsmouth veteran.
Terry's knee was, sadly, a problem waiting to happen. Since he first encountered difficulties last Wednesday, which ultimately ruled him out of the Estonia match on Saturday, his fate had rested on where his floating knee debris settled. Over the past eight days this debris – either loose cartilage or bone – has twice settled in the joint of his knee, which resulted in acute pain and swelling for Terry. It acts like a piece of grit in the eye, constantly scratching the surface of the bone.
He is out of tonight's match, just as McClaren hoped to be finalising his plans. In truth, Terry was never really right – he could not train on Sunday and was evidently playing through pain on Monday. It puts into perspective his words earlier in the day, before the injury resurfaced. "I have a very short career as a footballer and I want to make the most of that," Terry said. "If that means playing through a few injuries and a bit of pain, so be it. I don't want to look back when I am 35 or 40 and think I did not play the games I could have."
Not this time. England will have to line up as they did against Estonia on Saturday, with the only change being Joleon Lescott at left-back in the place of the injured Ashley Cole. That is another interesting decision from McClaren, whose back four now consists of a teenager, a 33-year-old, a left-back who usually plays centre-back and has never started for England – and Rio Ferdinand. If ever the Manchester United man needs to have the game of his life it is tonight.
So much of McClaren's reign has been blighted by injury it is not unexpected that he should have to encounter it again on this most significant of nights. Win and England are through to Euro 2008; draw and their destiny is still in their own hands. Should they lose, Russia would only have to beat Israel and Andorra to take the second qualification place behind Croatia.
McClaren was asked yesterday to draw comparisons with Brian Ashton's England rugby team and to describe what he saw as the archetypal English sporting hero. A starting point would be the kind of player who does not wear tights under his shorts – as many did at training in the chill Moscow air last night.
"The history and tradition of English teams and English individuals is never give up; never-say-die spirit when their backs are against the wall – they come out fighting and they come out on top," McClaren said. "Despite criticism they still stand up, they are still ready to be counted and they still deliver when necessary. Exactly like those last two rugby matches. We were all inspired by those, the players, myself and the staff included. That's what we need."
It may sound like the same old clichéd English attitude, but for McClaren the reaction of his players, especially during the laboured victory over Andorra in Barcelona in March, has been crucial. He believes he has seen a change in them and that they are developing at last into a serious side, with five 3-0 wins in a row in qualifying. It is one of the reasons that he has stuck with virtually the same XI tonight.
Guus Hiddink's Russia are expected to be much more adventurous tonight because, as McClaren pointed out, they have to win. "The pressure is on Russia," he said. "They have to win the game, they have to take risks. They're at home and they have to set the tempo."
"We need one of those performances we saw at the weekend from the rugby team and which we've seen from English teams in recent years: Istanbul  and Rome  come to mind. We need heroes out there."
Without Terry, and in a team who do not have the five men that Russia have in midfield, it will be quite a task. No one would have forgiven McClaren for picking an extra midfielder for this game, but he evidently believes that by keeping two strikers England will stretch the Russians at the back rather than grind it out with them in the midfield. It is an approach that deserves respect.
"I love big occasions and there are none bigger than this. The England way and the England mentality is that the bigger the game, the more we respond to it and the better we become." So said Terry, less than an hour before his knee locked. It is the big night and England have to do it without their captain.