FC Barcelona’s Lionel Messi suffered a torn knee ligament and will miss 7-8 weeks. (AP Photo/Manu Fernandez)

Barcelona squeezed out a 2-1 victory over newly-promoted Las Palmas this weekend, but the result was not the story of the game. Early in the first half, following a collision inside the box, Lionel Messi went down holding his knee.

He was quickly taken off the pitch, and tests revealed a tear of the medial collateral ligament in Messi’s left knee. That particular injury to the knee is typically not as serious as an injury to the interior (cruciate) ligaments, and Messi is expected to return by December.

[Barcelona’s Lionel Messi tears knee ligament, will miss 7-8 weeks]

Still, Barcelona will be without the world’s best player for two months. How will this affect the Catalan side’s treble defense?

The first question here is one of baseline. How good is this Barcelona team?

Hampered by a transfer ban this summer, Barcelona was unable to re-stock its squad with established stars. While Barca has started 5-0-1, the goal difference of just plus-4 looks unusual. Four of those five victories have come by just one goal. Last year at this time Barcelona had yet to allow a goal and had scored 17. Two years ago the numbers were 22 goals scored and five conceded. For the most part, however, the problem appears to be finishing rather than chance creation.

By expected goals, a measure of the quality of chances created based on location, assist type, the kind of attacking play leading to the shot and other factors, Barcelona is clearly one of the two elite clubs in La Liga. Early-season leaders Villarreal look like a fluke along the lines of Leicester City or West Ham in the Premier League, and we should expect the usual order to be resumed soon in Spain.

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But with Messi out, will that happen?

It is difficult to measure the impact of any single player on a team’s quality. One of the odder stats of the last five years is just how well Barcelona has played without Messi.

According to data from transfermarkt.com, Lionel Messi has missed 14 league matches due to injury since 2010. (I excluded matches from which Messi was held out for other reasons, as presumably a superstar would only be optionally rested either against weak opposition or when the outcome did not matter much.) In those 14 matches, Barcelona went 13-0-1 with 40 goals scored and only eight conceded. The expected goals numbers are almost exactly in line with Barcelona’s expected goals statistics in matches Messi started.

This does not mean Messi is not that great, nor that you can easily replace him with Cesc Fábregas or Seydou Keita and expect similar results. It means that in 14 matches, especially against weaker competition, patterns can be difficult to detect.

Barcelona has been fortunate with Messi’s injury, as he has not been held out of a Clasico against Real Madrid for injury, and basically all of the 14 matches came against lower- or mid-table opposition like Mallorca, Granada and Elche. This year Barcelona’s luck may hold again. Messi is sure to miss five matches, and three of the clubs Barca will face in that time (Eibar, Getafe and Rayo Vallecano) do not look like serious threats. Villarreal and Sevilla should pose tougher obstacles. The big risk comes later, as Messi’s 7-8 week timeline specifically leaves open the possibility he could return for the November 22 Clasico.

To estimate how much losing Messi might hurt, I ran some simulations and compared the expected points for Real Madrid and Barcelona over their next seven matches. It is hard to guess what the size of the effect will be. Barcelona will likely be depending on La Masia graduates Munir El Haddadi and Sandro Ramirez to fill in at forward, and there is little evidence from which one can project their likely performances. So I tested out three possibilities: that losing Messi weakens the Barcelona attack by 30, 20, or 10 percent, and weakens the defense by a bit as well.

At full strength, Real is favored to take about one more point than Barcelona in the next seven matches — Real has slightly better stats and a slightly easier schedule. If losing Messi makes Barcelona’s attack about 30 percent worse, then the gap jumps to about four points. If Messi makes them 20 percent worse, Real should take about three more points over the next two months, and at 10 percent the gap would be two points.

This helps explain why it is so hard to identify Messi’s value from the time he is off the pitch. Because La Liga is so unequal and Barcelona so good, Barca remains strongly favored in most of its matches even if the club is significantly weakened. The expected point gaps can be measured on the fingers of one hand, even in scenarios where Messi’s effect on his team’s quality is legitimately massive. Unless the loss of Messi causes an unexpected, utter disaster, Barcelona should be easily within striking distance of the title when its superstar returns.