History can turn on the seemingly least consequential of events. On April 12th, 2015, Manchester United were leading Manchester City 4-1 at Old Trafford with three minutes remaining when Michael Carrick rolled an ankle on the touchline and limped off. Sergio Aguero pulled a goal back for City but of far more significance was that Carrick was ruled out for the rest of the season.

It was United's sixth Premier League win in a row, a run in which they had beaten not only City but also Liverpool and Tottenham Hotspur. It was the best they had played under Louis van Gaal.

Everyone had been waiting for the click, the moment at which United assimilated his philosophy, the cogs aligned and fluency ensued, just as his Bayern Munich side had suddenly won 4-1 at Juventus in the group stages after months of unconvincing striving and had gone on to win the German double and reach the 2010 Champions League final. Was this United's equivalent?

Perhaps it would have been – probably not – but without Carrick, United won only one of their final six games of the season. United had been third, pushing for second.

If they had beaten Chelsea a week later they would have been five points behind the tiring league leaders and an implausible title charge might have been, if not likely, at least conceivable. As it was, they finished fourth.

But the issue, really, is not what United might have done, it is how important Carrick remains to them. In 2014-15, United picked up 2.44 points per league game Carrick started, as opposed to 1.41 when he did not. Last season United got 1.91 points per league game he started – 1.50 when he did not. This season Carrick has started five games in all competitions. United have won them all.

Pattern is consistent

There are caveats. Not all games are equal. Jose Mourinho has tended to play Carrick in the easier games. The midfielder has started only one Premier League match, the 3-1 win at Swansea City on November 6th, but the pattern is consistent over time and there was no sense Van Gaal spared him the tougher matches.

Carrick is 35; he is manifestly not the future. Even if physically capable of playing in every game, which seems unlikely, it is necessary to look beyond the immediate but it is perhaps worth asking just what it is that makes him so valuable. Why are United better with him? What do they lack when he is not there?

Most obviously there is his passing. Carrick has played only 102 minutes of Premier League football this season but his pass-completion rate of 96.6 per cent is remarkable. Throughout his career he has averaged in the high 80s.

He offers a measure of control and authority and, in so doing, protects a back four who have looked jittery this season – and are likely to remain so as long as Marcos Rojo is around.

Critics will say Carrick was the perfect Van Gaal player, someone who passed the ball endlessly sideways, registering impressive possession stats without going anywhere. It is an allegation not without foundation but misses an important point about balance.

Having one player who can be relied on to keep the ball is not the same as having 11 who are terrified of giving away possession. As he showed this season in the home win against Fenerbahce, Carrick is more than capable of incisive 40-yard forward passes when the situation allows.

Natural holder

Carrick is not perhaps the most fashionable player. It is hard to see how he would fit in a hard-pressing, relentless running team such as Liverpool, Chelsea or Tottenham. Yet Pep Guardiola brought in Xabi Alonso, a similarly experienced midfield lubricant, at Bayern, favouring possessing as well as pressing.

Alonso also played for Mourinho at Real Madrid. He and Carrick are not identical but there is a similarity of approach. Mourinho may instinctively prefer more dynamic players but a natural holder, someone with the positional sense to guard the central defenders, a range of passing and the intelligence to use it will always have value.

There is a psychological aspect as well: Carrick, with his demeanour and his style of play, projects confidence. In a team doubting themselves, his calmness can benefit all around him – an attribute that could be useful at home against Arsenal on Saturday.

The issue is Carrick’s age and what his regular inclusion may suggest about United’s transfer strategy and planning. When you spend as much as United did in the summer, you do not expect to be relying on a 35-year-old who has been at the club since 2006.

Given how things have started perhaps Mourinho and United are not in a position to be picky. Whatever the long-term strategy the fact is for now United play better when Carrick is involved. Guardian service