The Manchester City forward limped off and has clearly been unfit for much of the tournament, leaving the main man to take on even more of the attacking burden
By the standards of any World Cup, Argentina's group is a modest one. You can of course only defeat what's in front of you and Messi has been able to do that with relative ease. But the concerns about the form of his attacking colleagues remain. Gonzalo Higuain has seemed woefully off the pace, and almost reluctant to get involved. But the main issue is Aguero.
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The Manchester City man is an exceptional footballer, but his hamstring and calf problems continue to stunt his development into a bona-fide world star. The tantalising prospect of him playing in tandem with Messi at this tournament has been replaced by frustration, and, ultimately, submission to yet another setback.
In the 38th minute the stretcher was out, but Aguero chose to limp into the dugout. Irrespective of whether he is able to play a further part in this tournament, it's clear that he wasn't fit beforehand, and he most certainly isn't fit now.
There's two schools of thought - the first being that in the knockout stages, higher quality teams will play in a more open, expansive fashion, leaving space for Messi and the front four to showcase their exquisite counterattacking ability.
The second is that Iran performed manfully for 92 minutes and had it held out for 30 seconds longer, the nation would have restricted one of the favorites to little more than long-range efforts. Other opposing sides may take a similar approach given the relative form of Messi's teammates. Flood the space around Messi, and you stop Argentina.
Sabella is well aware of it, but seems willing to accept it.
"Every time you have a player like Messi, there is of course overdependence," he said on Tuesday.
"We try to reduce that but you have to depend on him. I guess this is normal pressure for a player and we try to reduce the pressure on him by playing together."The pre-tournament build-up was all about Messi and how he would shine on this stage, something that he's achieved with distinction so far. But the real driver behind Argentina being touted as potential winners was the dynamism and fluidity of the front four as a collective. That hasn't been in evidence here.
That being said, the Messi of the opening 45 minutes against Bosnia-Herzegovina is light years from the Messi who left to a standing ovation against Nigeria. From a sullen, disinterested figure, the sparkle is back and the fleet of foot is once again in evidence. He looks ready to take on the tournament. At this point, he may well have to.