Antoine Griezmann
Griezmann could have joined Chelsea last January but Mourinho baulked at the fee. Getty

He floats like a butterfly, he stings like a bee and he is the stand-out player of La LIga this season. However, not everyone is surprised by Antoine Griezmann's explosion at Aletico Madrid.

Griezmann was the key protagonist in Real Sociedad's journey from second division to Champions League in just four seasons, and has carried on where he left off in Madrid, scoring 25 goals this season - 22 in La Liga. That puts him just behind Cristiano Ronaldo and Lionel Messi, two of the greatest players of this or any other era, in the Spanish scoring charts.

Griezmann's figures look even more impressive when one considers that he scored just one goal during the first three months of competition. His evolution since then has been astonishing and the Atletico aficionados are frantic with worry that he might leave this summer. Jose Mourinho signed three Atletico stars last summer - Thibout Courtois, Filipe Luiz and Diego Costa. The threat - and the fear - remains in Madrid.

Several Spanish and British newspapers have noted Chelsea's interest in signing the French international during the next few months, in a deal that would include the payment of a buyout clause set at £40 million.

This is not just a rumour; in fact the story began a year and a half ago, as we know well in San Sebastian.

In January 2014, when it was a badly-kept secret that the former Real Sociedad player was moving to another club during the summer, Mourinho and Chelsea tested the water. They contacted the Basque club's offices and the Portuguese phoned Esteban Granero, the former Real Madrid player with whom he has a strong relationship.

Cristiano Ronaldo

'It is sad to accept that, after his retirement, Ronaldo will be remembered for his outstanding stats and trophy haul, but also for an attitude that, for from hurting him or his teammates, has made him one of the best players in the history of football.'

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Mourinho was intrigued by the outstanding level shown by Granero's left-footed team mate at Real Sociedad. Above all, he wanted a reference for Griezmann's professionalism after an incident that took place during a French under-21 training camp two years earlier, when Griezmann left the hotel at night with a group of players and took a taxi to a club in Paris. Several photos were published on social media and Griezmann had to pay the price: a year out of the French national squad.

Mourinho was worried Griezmann might be a dilettante, but, as Granero told him, nothing could be further from truth: Griezmann loves training and is happy to do the physical work, to the extent that he has lost nine pounds while gaining muscle in the gym.

So when Chelsea's manager listened to his former player's opinion, he realised Griezmann was the player he was looking for. A superb player, fast and incisive, who puts fear into the most accomplished defenders.

Mourinho made an approach during the last week of the 2014 winter transfer window, but went no further. The Portuguese decided not to follow up his enquiry upon realising that the only chance of signing Griezmann involved a £24 million expenditure. Too much for a player who had not prove his skills in a top European club.

Instead, he signed Mohammed Salah from Basel for £11m. Both of them played in the left wing at that stage. The decision looks more and more misguided by the day.

'There was movement - but they thought it was a high price'

Griezmann's agent, Iñaki Ibañez, alluded to the interest in an interview with IBTimes UK, telling us: "Last season, there were various top-level clubs from the Premier, the Bundesliga and the French league showing interest. There was movement. What happened is that the player, although he had demonstrated his level at Real Sociedad, hadn't done it in the elite of European football.

"In these circumstances, some suitors were willing to pay the price, but the great economic state of Real Sociedad demanded that they pay the full release price. The interested parties thought it could be a very high price for someone who hadn't yet competed regularly at the highest level."

Despite choosing not to pursue his interest in Griezmann, Mourinho had a hunch and kept on spying on the Frenchman. West London scouts visited San Sebastian during last season's final games.

Just 16 months after that first approach, Mourinho has sent Salah on loan to Fiorentina, whereas Griezmann is La Liga's top scorer after Cristiano and Messi. Mourinho did not make the right decision, and obviously he would be happy to amend the error.

Would Griezmann fit into today's Chelsea? Absolutely. Let's think about Mourinho's squads during the last decade. He always looks for players who show loyalty and commitment on and off the pitch. Players who believe in a footballing ideal and show engagement with it, sometimes at the cost of a decline of individual performances. That is why Mourinho keeps an eye on Simeone's Atlético de Madrid, a footballistic philosophy that involves the same kind of players and spirit. That is why Griezmann would fit the bill.

When it comes to tactics, Griezmann would be the perfect player for Chelsea. He played his first seasons at Real Sociedad on the left wing but he was out of place, as he makes the most of his skills behind the striker - Oscar's position in the current Chelsea team would be tailor-made for the Frenchman.

Anyway, Griezmann is very versatile and he even stood out playing in the midfield, in Cesc's position, under the tenure of Philippe Montanier. Some seasons later, he does everything, and everything right. He is infalible in one on ones, one of La Liga's fastest players with the ball at his feat, and he recovers possession very often, a very rare skill when it comes to a forward.

Mourinho, one of the world's shrewdest managers, doesn't want to make the same mistake twice. Few would bet against him swapping red for blue this summer.

Oier Fano Dadebat is a Spanish journalist who divides his time between San Sebastian and London. You can find out more about him on Twitter @oierfano.