The Premier League kicked off last weekend with most of the top        contenders failing to put on a good show – Man United beat Spurs only because of Kyle Walker’s carelessness, Liverpool had Coutinho to thank for a late winner, and Arsenal were outgunned comprehensively, by West Ham United. Man City looked the sharpest, whacking West Brom soundly.

But what of the Champions? Chelsea’s all too familiar problem, a lack of firepower, reared its ugly head once again. The Blues spluttered to a 2-2 draw against a Swansea side that looked set to get an unlikely victory at the Bridge, but was more than happy with the point at the end.

However, not bolstering their strike force may not be the only mistake that may come back to haunt Chelsea later on this season. They’ve let a few key players go over the years, who may all prove to be the difference between Chelsea being Champions again or ending up as also-rans. We take a look at some of the best who got away.

5. Juan Mata

The 2012 and 2013 Chelsea Player of the year was unceremoniously dropped by Mourinho at the start of his second reign as the Blues boss. Blamed for “not working hard enough”, Mata was given very little playing time, causing the Spaniard to ask for a switch to Old Trafford. Moyes didn’t prefer him too much, and in LVG’s constant chopping and tossing, there were fears that the true Mata may have been lost. However, despite a slow start to his time in Manchester, Mata has grown to become one of United’s most trusted servants. Possessing the “brains” that are so crucial for a modern day central midfielder, Mata has provided his teammates with the ammunition that propelled them back into Europe after a year in the wilderness. Also chipping in with crucial goals from time to time, Mata may well prove to be the difference for this new look Man United side as it seeks to re-establish itself as Champions of England. Chelsea should be wary.

4. Andre Schurrle

Andre “Super Sub” Schurrle has definitely mastered the act of being in the right place at the right time. Time and again, for both Chelsea and the German national team, Schurrle has been introduced to provide the spark that his teammates have been unable to provide despite toiling for long. Being Rusty after his World Cup exploits, Chelsea seemed to think that the German has lost his mojo and sold him to Wolfsburg in favour of getting a direct replacement in the form of explosive Colombian Juan Cuadrado . That move seems to have backfired, it seems. Cuadrado has failed to settle into the side, proving grossly ineffective compared to Schurrle. If there is anything the Chelsea pre-season seems to suggest, it’s that this side will struggle to find goals this season. In such a scenario, Schurrle could have been useful.

3. Filipe Luis

Filipe Luis was signed by Chelsea to fill in for the departing Ashley Cole at left back. Little did he know that Jose Mourinho would continue to favour out-of-position Cesar Azpilicueta over him. Indeed, opportunities were few and far between for Luis but the former Atletico Madrid player filled in cheerfully whenever required, with any fuss over his lack of starts. The opportunity to rejoin the former Spanish champions, however, was too good to resist. Now the Brazilian is gone and Chelsea are left staring at a hole in the area that they pride themselves on- defence. Defenders are prone to injuries and suspensions and a particularly bad set of circumstances could see the Blues exposed. They need to sign a replacement, and quick.

2. Kevin de Bruyne

De Bruyne has got to be the hottest young talent in the Bundesliga at the moment. Named “Footballer of the Year” in the Bundesliga last season, De Bruyne has blossomed into a creative whiz at Wolfsburg with the kind of freedom he would never have enjoyed at Stamford Bridge. Scoring 13 goals in 50 appearances for the German side, and setting up countless more, De Bruyne has become the kind of player who single handedly destroys the opposition given the time and space. No wonder Man City are desperate to sign the 24 year old! Manuel Pellegrini has had two bids rejected, but it’s unlikely the Chilean will stop before he has added the Belgian to his already burgeoning set of attacking players.

1. Petr Cech

In Cech’s case it’s not about what the Blues have lost but about what their opponents have gained instead. Petr Cech is one of the absolute legends of the Premier League, keeping the ball out of the Chelsea goal for what seems like forever. While they do have a more than adequate successor in Thibaut Courtois, Chelsea should not have sold Cech to a direct rival. Arsenal have gained a proven match winner, someone who can prove to be the difference between two points lost and three gained. He may have come unstuck during their season opener against West Ham, but Petr Cech will only make Arsenal stronger and when it comes down to the title race, Chelsea may have handed their London rivals the edge that they have sought for so long.