What makes a great defensive unit? Of course, a natural gift and individual ability are the cornerstone of any footballer’s skillset, but perhaps just as importantly, cohesion, continuity and a collective understanding are all traits that the country’s best defensive set-ups have traditionally thrived on. And for the goalkeeping element of the rearguard in particular, these traits couldn’t possibly ring more true.

Hence why Sir Alex Ferguson’s current penchant for rotating his goalkeepers, seems to go against definitive defensive logic. The pair of David de Gea and Anders Lindegaard are both brilliant goalkeepers but still appear to struggle with defining aspects of the English game. There may be little to pick between the two, but the only way either De Gea or Lindegaard are truly going to be able to adapt in the long-term, is by playing long, hard game time.

Sooner or later, Fergie is going to have to put his eggs in one of their baskets.

It’s easy sometimes to forget the respective ages of Manchester United’s fledgling goalkeeping duo. The rakish David de Gea will celebrate turning the grand old age of 22 in six weeks time and his Danish counterpart Anders Lindegaard, is only 28. In goalkeeping years, Lindegaard isn’t even near entering his prime years yet let alone De Gea.

Before Joe Hart’s exploits in goal for Manchester City last season, the average age of a title-winning goalkeeper over the last 30 years in the top flight has been 31.3-years-old, rising to 32.7 in the Premier League era. But the notion is of course, if you’re good enough, you’re old enough. Yet blooding the pair of De Gea and Lindegaard into the Premier League hasn’t been a particularly easy task in itself.

Lindegaard arrived at Old Trafford in November 2010 for a reported bargain price of £3.5million. Of course, he wasn’t able to officially play for the Red Devils until January, but with United involved in a cutthroat Premier League title race and with the legendary Edwin van der Sar still at the helm, the big Dane was never likely to get a look in. A couple of cup cameos were all his season amounted to till the 2011-12 term, during which he’d be competing with quite literally, a new boy on the block.

The acquisition of David de Gea for fee of around £17million was big business and United weren’t necessarily acquiring a goalkeeper who was worth nearly five Anders Lindegaard’s, but the premium wasn’t just locked in his potential. Despite the fact that he could potentially offer near on two decades of service to United, in which case that fee would work out as peanuts, his gifted reflexes and shot stopping ability needed no development. De Gea’s talents already served Atletico Madrid adequately to a Europa League trophy, a Uefa Super Cup and a seventh place La Liga finish.

Yet the defining issue was that Manchester United were starting the 2011-12 season with two goalkeepers, three if you include youth product Ben Amos, who had never kicked a ball in the Barclays Premier League before. The shot-stopping berth was never going to come trouble free for Fergie last term and so it proved at points last season.

David de Gea started the term as United’s number one and as talented as he may be, the teething process appeared a little too painful to take at one point last term. A clichéd yet notable deficiency in dealing with aerial confrontations, saw the Spaniard dropped for his Danish counterpart. Lindegaard seized his initiative after making his league debut in the 2-0 win against Norwich last October before embarking on a steady, if not unspectacular run in-between the sticks for United. It was only a cruel twist of fate in the shape of ankle ligament damage at the start of the year that saw De Gea return to the line up.

The ex-Atletico man produced a superb run of form and marked improvement in his game to end the season on a high and it’s important to note just where United finished last season. For all the high profile dissection of their goalkeepers, they only lost the title on goal difference. Yet last season has ensured that again, United started the term with a set of goalkeepers yet to complete a full Premier League term in goal. And this is where the issue lies.

Following De Gea’s perceived mistake that ended in Nemanja Vidic’s own goal during 3-2 win over Fulham last month, again it was Lindegaard that stepped back into the fray. Fergie had somewhat papered over the situation by determining his selection policy as ‘rotation’. Speaking earlier this month, he said:

“I think the most important thing I'm trying to achieve is experience of the English game.

 "They are both young, they don't have the experience of a Van der Sar or Schmeichel, so alternating is not a problem for me.”

But in juggling both De Gea and Lindegaard around, neither are getting the full benefits of the English game. Bringing in De Gea for the Galatasaray game in the Champions League was noble but it was academic in terms of him making any form of long-term claim for the number one jersey. He’s already shown he is perfectly adept at performing in European competition for both United and Atletico. He’s not going to get any better at dealing with the likes of a Grant Holt or Andy Carroll in the air by playing in the Champions League.

And likewise with Lindegaard, there is something of a ‘what you see is what you get,’ sort of feeling with the Dane. His current performances are an extension of what we saw in glimpses last season, in that he’s solid rather than spectacular. He seems to offer consistency rather than perhaps the God-given gifts of De Gea, but if that’s what Fergie craves, than dropping him isn’t going to achieve anything but unsettling the defence for an umpteenth time.

David de Gea’s flaws are fixable and as we saw last season, he isn’t a million miles away from flushing them out of his game. But no amount of coaching, training ground work or European competition can ever substitute for Premier League playing time. The only way he can improve is by playing.

But it is the team that will ultimately suffer if Fergie continues to sit on the fence. The United backline needs an identity and a strong foundation. That can only come through consistency and continuity and he has to stick with either De Gea or Lindegaard soon. It’s time for Sir Alex to put his faith in one his keepers and back them to the very hilt.

Who would you play in goal for United? Is Fergie right to continue to rotate his goalkeepers? Let me know what you think on Twitter: follow @samuel_antrobus and bat me all your views.