The transfer window is always good to analyze, but it's always intriguing to discover the methodology behind a football club's decision to sign a player.
It can have many variables, such as how many goals a player scored, how many they assisted, what's their pass accuracy percentage and even, how many bookings did the player get.
But one of the most important factors, by far, is whether a player performs or scores against you. It's the ultimate way of determining whether a player is suitable for your side by matching up his ability to your team.
Though many managers would outright dismiss it as the underlying reason for signing a player, there's an undeniable pattern that has emerged in recent years to show it is true.
Chelsea are an advocate of this rule, having finally signed Andre Schurrle this summer after two years pursuing the Germany international, following his impressive performance against the Blues in the Champions League for Bayer Leverkusen.
And it appears they could adopt a similar approach as they look to add the final jigsaw piece to their puzzle. The only problem is that he is Wayne Rooney, who is viewed as indispensable at Manchester United and will not be sold to their Premier League rivals, per Sky Sports.
The 27-year-old striker, who came on to produce an assist in the 4-1 win over Swansea on Saturday, cut a forlorn figure as he walked back to the centre on his own while his teammates celebrated a goal. And it's that sense of isolation which shows how he is still set on a move away from Old Trafford.
For many years, Rooney has terrorized the Chelsea defenders with important goals, and it's a known fact that the Blues are one of his favorite teams to play against, having scored nine goals against them in his nine years at Manchester United.
Supposedly, the justification Roman Abramovich may use for the reason of signing the £40 million-rated forward is that if you can't beat them, sign them. The worrying aspect of this transfer saga is that recent history shows the Russian usually gets his man in the end.
That said, new boss David Moyes is continuing to resist Chelsea's approaches, having already rejected two bids, per BBC Sport. Despite Jose Mourinho's admission that he will fight "until the end of the window" to secure Rooney, per The Telegraph, it's highly unlikely that the Portuguese boss will chase the England international without having a back-up option.
That's where Samuel Eto'o comes in.
The 50-year-old coach brought the Cameroonian veteran to his old club Inter Milan from Barcelona when he took over in 2008, and somewhat inevitably, it was an inspired signing.
His impressive haul of 37 goals in 53 games in all competitions was important in helping the club secure a magnificent Treble in the 2009-10 campaign, and Eto'o enjoyed a close relationship with Mourinho during his two seasons at the San Siro.
There's no prizes for guessing why he would want to work with Eto'o for a second time. A pacy, hard-working striker who manages to score goals wherever he goes, the 32-year-old is one of the most lethal finishers in World Football, having scored 55 goals for his country from 112 caps.
Surviving members of Chelsea's team that played Mourinho's Inter side in the Champions League in 2010 will know exactly what he can do, having scored the winner at Stamford Bridge which consequently sent Carlo Ancelotti's side crashing out at the quarterfinal stage.
A strong forward with incredible levels of fitness, Eto'o may not be as nimble as he was three years ago, but still has the intelligence to make dangerous runs in behind the opposition defense,.
Needless to say, with their playmaker Juan Mata certainly capable of playing an accurate pass, it could be a deadly combination should the Blues decide to move for the four-time African Player of the Year.
Some critics will ask why the West London club are pursuing a fourth striker when their formation resides around playing a lone striker with wingers as supply lines. Fernando Torres, Romelu Lukaku and Demba Ba are the current options for Mourinho, and the majority would be satisfied with the amount of firepower in the squad.
But the answer lies with Ba, who has been linked with a move away from Chelsea just eight months after arriving from Newcastle after falling down the pecking order at Stamford Bridge. If Mourinho could offload the Senegal striker, replacing him with Eto'o would be a shrewd piece of business.
Rather conveniently, Eto'o has seen his chances of a move away boosted after his club's owner Suleiman Kerimov decided to drastically slash the budget, with several stars already on their way out, per The Guardian.
His interest in joining Chelsea looks to be genuine, as he was quoted in The Mirror as saying, "Chelsea are a great team. When we have all the offers on the table then I will discuss with my agent and see what my next step is.”
That said, there are concerns about Eto'o's suitability and adapting to a new league when approaching his final years as a footballer. Questions over whether he can now handle the intensity of the Premier League will forever go unanswered unless he signs for an English team.
Given the swift decline in pace he has experienced during his time in Russia, it somewhat explains why he has managed a paltry 25 goals for his current club Anzhi Makhachkala in his two seasons at the club.
Additionally, considering the impact it would have to bring the 32-year-old to Kings Road, who currently earns £300,000 per week and would cost in excess of £10 million, the financial aspect of the deal could be an obstacle. As a result, the Blues would probably demand that he drops his wage demands in order to secure a dream move to the Premier League.
Given that Chelsea's efforts are fully focused on bringing Rooney to the club, with a third and final bid of around £40 million offer lined up, per Sky Sports, the potential arrival of Eto'o could fail to materialize once again.
Even at this stage, it is just speculation, as Miguel Delaney from ESPN reports there has been no formal contact from the club to Eto'o's agent.
Nevertheless, if Chelsea could swoop for Rooney, who has been a constant thorn in the side to them over the years, it would be yet another sign of how Mourinho seeks to weaken his rivals.
Sign Eto'o, though, and Chelsea could well be champions for the fourth time by the time May comes around.