Costa returns as Casillas braces himself for fiery reunion
As unpalatable as it can be, Chelsea manager Jose Mourinho needs his fighters right now and it is apt that his ultimate warrior Diego Costa returns to face the man who was cast aside for being a peacemaker.
Among the familiar faces Mourinho will encounter for his latest return to Porto will be goalkeeper Iker Casillas, who will set a new Champions League appearance record by facing Costa and Chelsea.
Retrospectively banned in the Premier League for his clash with Arsenal's Laurent Koscielny, Costa is free to play in Europe and Mourinho will not attempt to curb any of the striker's aggression.
In the world of Mourinho, you are either with him or against him, there is virtually no middle ground, and the Portuguese is loyal to those who he believes are willing to sacrifice themselves for the cause.
Costa very much falls into that category, while Casillas stood accused of disloyalty under Mourinho at Real Madrid and controversially lost his place.
During Mourinho's reign at the Bernabeu, matches between Real and Barcelona turned into all-out war.
Relationships between the Spanish contingents of both teams were strained until Casillas, the Real and Spain captain, attempted to ease the tension by meeting Xavi and Carles Puyol. But the peace pact ended with Casillas losing his Real place to Diego Lopez.
Harmony with his rivals is not what Mourinho is about and the Casillas episode helps to explain why he will not criticise Costa for doing whatever he can to gain an advantage for Chelsea, even if he occasionally crosses a line.
Casillas never recovered from the fall-out with Mourinho at Real and eventually joined Porto this summer.
The 34-year-old equalled the 151-game Champions League appearance record set by former Barca midfielder Xavi by playing in the opening Group G draw with Dynamo Kiev.
On his relationship with Mourinho and the way his Real career ended, Casillas, who has won the Champions League three times, said: "It was like being in a couple. In the end it disintegrates. You start well at the beginning and later on, you don't have that feeling that you had before."
The feuding between Mourinho and Casillas did not stop when both men had left Real. Mourinho described his Porto wages as "amazing", which made front page news in Spain. But he shot himself in the foot as Porto are paying less than a third of his salary - Madrid pay the rest.
Whoever pays, Mourinho is a win at all costs kind of a guy. Costa gets that, Casillas did not.