World Football's 9 Most Costly Injuries of the Season

It doesn't matter if you're fighting for survival or chasing multiple trophies and are sat at the top of the league—an injury to a key player can make or break your season.

With a better understanding of the human body and better doctors and physical therapy available at a moment's notice, players are protected infinitely more than they were 20 years ago.

Gone are the days when a player with a broken neck would see a game through until the end as the financial risk to the club is just too great.

Here we'll take a look at some of the worst injuries that have been seen in some of the top leagues this season and how they may affect the parent clubs' performance.

Manchester United defender Nemanja Vidic is out for the rest of the 2011-12 season after rupturing a cruciate knee ligament.

The missing defender will be a huge blow to Manchester United's title chances as they attempt to decrease the deficit between them and neighbours Manchester City.

Vidic's agent denied that the defender may consider retirement because of surgery resulting from the injury.

Liverpool's defensive midfielder, Lucas Leiva, is also out for the remainder of the season after injuring his anterior cruciate ligament in a Carling Cup match against Chelsea.

Liverpool do not have a ready-made replacement for Lucas as Jay Spearing has yet to really find his feet in the Premier League and it has been suggested manager Kenny Dalglish may look to replace the midfielder in the January transfer window.

Lucas has increased his standing on Merseyside considerably since his days as a Kop boo boy.

Barcelona striker David Villa suffered a horror injury when he snapped his shinbone in a Club World Cup game.

For those of you who aren't squeamish, you can watch the video here.

Villa is expected to be out for approximately five months whilst he recovers from surgery.

Barcelona are seemingly missing the Spaniard's firepower as they find themselves five points adrift of rivals Real Madrid.

Arsenal defender Bacary Sagna currently has a broken leg and has missed most of Arsenal's games so far this season.

Sagna landed awkwardly after jumping for a header against rivals Tottenham and suffered the broken fibula.

Arsenal have missed the Frenchman considerably and they have since suffered a defensive injury crisis, covering almost all of their usual starting back line.

Manager Arsene Wenger will need Sagna back and playing if he wants to qualify for the Champions League next season.

Manchester United midfielder Darren Fletcher has been diagnosed with ulcerative colitis, which is a disease of the large intestine.

Fletcher has been ordered to take a full break from football in an attempt to rid himself of his problems, which will hopefully be cured by taking anti-inflammatory medications and rest.

Manager Sir Alex Ferguson recently had to persuade 37-year-old Paul Scholes to come out of retirement in order to provide some midfield cover for his injury-hit side.

AC Milan striker Antonio Cassano had to be hospitalized this season after he fell ill after Milan's 3-2 win over Roma.

Cassano was diagnosed with ischemic-based cerebral damage, which meant he had to undergo surgery to repair an atrial septal defect in his heart.

The injury left Milan short on attacking options and they will be hoping Cassano will return to first-team action soon.

Seemingly not content with one freakish injury problem to their squad, AC Milan were blessed with two problems after defensive midfielder Gennaro "Rhino" Gattuso suffered an eye injury.

Gattuso suffered a paralysis of the seventh cranial nerve after he collided with a teammate but has recently returned to first-team action.

At one point it was unclear whether Gattuso would ever play football again.

Barcelona forward Ibrahim Afellay is another player who injured his anterior cruciate ligament this season and he underwent surgery toward the end of 2011.

Afellay has faced a number of injury setbacks for Barcelona, and the Catalan giants are certainly missing his attacking threat.

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Bayern Munich lost star midfielder Bastian Schweinsteiger in November to a broken collarbone which may hamper their attempts to win the league.

On the plus side for Bayern in might keep the January vultures away until the Summertime following speculation that Manchester United and Chelsea were keen on signing the German.

Considering a large majority of people are happy to have time off due to a work-related injury, it never seems to be that way with footballers.

Those at the top of their game don't know anything else other than to kick a ball around for 90 minutes in an environment akin to that of the Roman gladiators.

The adulation and love from the fans is half of their reason for getting out of bed in a morning, and if that's taken away—either briefly or permanently—a part of their personality seems to go with it.

Just recently former player Dean Windass spoke out about his problems dealing with depression since leaving football, and he's certainly not the first to feel that way.

Whilst the injuries listed here aren't the worst ever seen on a football pitch, you never know which ones might cut players' careers short.

Cassano and Gattuso must have had all sorts of thoughts running though their minds when diagnosed with their respective problems, so fans should never take for granted the opportunity to see a great player in action.

Thanks for reading.

Follow me on twitter @petercwebster and click here to see some great goals by a World Cup legend.