Atletico Madrid v Chelsea: Jose Mourinho must first stop Diego Costa before he buys him

The Brazilian-born Spaniard will be the main threat this week

“It’s the most important goal I’ve scored,” says Atletico Madrid striker Diego Costa whenever he’s asked about his strike in last season’s Spanish Cup final against Real Madrid.

Cutting between Sergio Ramos and Michael Essien he ran on to a Falcao pass and shot past Diego Lopez to help Atletico win the game 2-1 and make a lasting impression on Real’s Jose Mourinho, now the Chelsea manager he faces on Tuesday night, and the coach he could be playing for next season.

There is an air of inevitability about Costa’s departure from Atletico. “We can compete on the pitch, but not financially,” says coach Diego Simeone.

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Atletico have seen Sergio Aguero and Falcao leave in recent seasons but Simeone has become resigned to it: “Falcao comes to you with an offer from Monaco and what are you going to say? You can’t say no to someone who has given you their life on the pitch. If Costa (below) decides to go then I’ll be the first to say: ‘That’s fine’.”

If Chelsea get their man in the summer, those who know him well say they will be buying character as well as quality.

The journeyman start to Costa’s career has taken him from Brazil to Portugal to four clubs in Spain – and the coaches and players he has played for and with are not at all surprised by his progress.

Swansea’s Michu was with him during a last-game relegation-escaping season at Rayo Vallecano. He says: “He already did a lot of things that made you think he was a player that would end up playing at the very highest level. He was frightening in training sometimes because he’s a bit mad, but as a person you couldn’t meet a nicer guy.”

José Luis Mendilibar who coached him at Valladolid when he was just 19, paints a similar picture. “He lulls people into a false sense of security,” he says. “He doesn’t look particularly quick, or technically that good. Sometimes it seems that he is one step away from losing the ball but somehow it stays with him and usually ends up in the back of the net.”

Costa has scored 34 of Atletico Madrid’s 107 goals this season and he is not just a goalscorer but the scorer of important goals. “Fans look at the goals-scored columns but coaches look at what kind of goals a striker scores” says Mendilibar. “Costa is one of those players who scores the opening goal that breaks the opposition down or the only goal of a tough 1-0 win.”

There have been times when indiscipline has tarnished good performances and left doubts over how far he might go. He was sent off last season for a head-butt in the Europa League and banned for four games, but Mendilibar says off the pitch Costa never caused him a moment’s grief.

“Of course he has that little bit of nastiness that all strikers need and it is important that he doesn’t lose that because it is a big part of his game. But he’s clever with it. He knows when to step back from the edge if he has a yellow card. And off the pitch he’s a calm guy. He undergoes a transformation once he crosses the line.”

The slow rise to stardom has also contributed to his character. Named after Diego Maradona by his football-mad father who gave all his sons footballing names, Costa’s dad was against him moving to Portugal aged 15 having heard horror stories of young Brazilians players dumped by unscrupulous agents when they failed to make the grade. But Costa persuaded him that his deal with the agent Jorge Mendes was to be trusted and the player moved, playing for FC Penafiel and Sporting Braga before switching to Spain.

Then came three loan spells and Mendilibar says: “He has benefited from not being thrust into the spotlight at a very young age. It has all been very gradual and he has had to work hard to climb the ladder. He was happy to be loaned out when he was a young player at Atletico. He has served his apprenticeship. No-one has ever given him anything and that has marked his personality.”

His form this season has persuaded Spain coach Vicente del Bosque to make him part of La Roja’s World Cup defence. “If people believe in me then I respond to that and deliver,” says Costa. “The more responsibility I have had at Atletico Madrid the more productive I’ve been.”

Could he respond to the demands of a move to Chelsea and the challenge of being the striker they, and Mourinho, have missed since Didier Drogba left?

“He is half a team on his own at times,” says Mendilibar. “He has this capacity playing up front on his own to occupy an entire defence, but I think he’s a different player to Drogba. I think he’s quicker and that means he is better at running in behind teams.

“But you can see why a team like Chelsea might look at him,” he added. “Their style is not dissimilar to Atletico’s and it means he could go there and play a similar game.”

Tuesday’s Champions League semi-final will be a trial of sorts but there is a feeling that Mourinho has made up his mind about the player who helped deprive him of a trophy last season and could repeat the trick. Before he signs him, though, he needs to stop him.