No matter what happens at Atletico Madrid in the Champions League tonight, Thibaut Courtois will be forever in their debt.

The Chelsea goalkeeper faces the Liga side for the first time since his successful three-year loan spell ended in 2014.

Chelsea are renowned for their use of the loan system and few players have profited more than Courtois.

The 25-year-old spent just a day at Chelsea’s training ground after joining from Genk for £7million in 2011 before catching a plane to Madrid and starting his journey as a serial winner.

Simon Johnson previews Atletico vs Chelsea in Madrid

He told Standard Sport: “Both teams wanted to buy me but Genk wanted more money and Chelsea agreed to pay it. Even though I signed for Chelsea, Atletico were still interested in taking me on loan. 

“At first, people wanted me to go back to Genk [on loan] instead but I felt I had to push my boundaries and try to go to Spain, to a very good team and build something there. 

“In those three years, we won La Liga, the Europa League, the Uefa Super Cup against Chelsea and the Spanish Cup against Real Madrid. Unfortunately, we lost the Champions League Final in 2014 after Real Madrid scored an equaliser in the last minute of normal time. That still hurts a bit but I hope to win it with Chelsea.”

A medal collection was not the only thing Courtois gained from Atletico – significantly, there was an education both on and off the pitch.

He was just 19 when he arrived at the Vicente Calderon. At first, the goalkeeper was subject of good-natured humour within the dressing room.

He was given a team suit by the club, but it was far too small and the 6ft 6in Belgian stood out for the wrong reasons. 

And Courtois initially rode a bicycle to the training ground, but that soon stopped when it was taken apart by his new team-mates and the saddle was left in the middle of a pitch. However, his performances were no laughing matter and it was not long before Courtois earned the nickname ‘the Octopus’.

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Courtois looks back on those times with great fondness and said: “For a lot of reasons Atletico have defined my football career up to this point, even my personal life. I went from a kid to being a real man there.

“If I saw a 19-year-old in goal for Atletico now, people would say that’s crazy. But I did an amazing thing and that’s why I say it defined me a lot. 

“I remember people saying that Atletico wanted me, that they are a big team and that it will be a big challenge for me. I don’t know why, but I just felt really prepared for it, really confident. 

“I went there and tried to do my best in training, as well as learn the language really quickly. That was important, I think.”

More crucial to Atletico was the arrival of Diego Simeone in December 2011. 

The club were just four points above the relegation zone and had been knocked out of the Copa del Rey by Albacete, who were in the third tier of Spanish football. Atletico have been on the rise ever since. Given Simeone’s animated behaviour on the sidelines during matches, intense work ethic and how well organised Atletico are defensively, the former Argentina international has a lot in common with Chelsea coach Antonio Conte.

Taking command | Courtois in action for Atletico against Chelsea in the Champions League three years ago Photo: Darren Walsh/Chelsea FC via Getty Images

“They are similar in many ways and are both fantastic managers,” Courtois said. “They are both very passionate, but Antonio has a different way of doing tactical training than Simeone. When Simeone came in halfway through the 2011-12 season, he built our team again.

“We struggled a bit in the first few months, but we went on to do very well. When I arrived at Atletico, at that point they were not so strong. I think they’d won the Europa League a few years before [2009/10], but after Simeone we got better and better. 

“People now see Atletico as one of the top teams in Europe and what Simeone has built at Atletico is really amazing.”

The club’s new ground, the Wanda Metropolitano, is pretty special, too, and will provide some venue for Courtois’ emotional return. 

English football has seen a few examples of clubs leaving their traditional home for a bigger site only for performances to suffer.

The Vicente Calderon stadium was a bear pit for opposing teams to try to play their football, but Courtois believes Chelsea will find a similar hostile environment at the new 67,000-capacity arena.

He said: “It may be their first game in the Champions League at the new stadium but that doesn’t make it a good time to play them. 

“They have already won twice there in La Liga, against Malaga and Sevilla. They have adapted very well. 

“The players are really happy and you can see that the fans are, too, because the atmosphere is amazing. They have transferred it from the Vicente Calderon already. 

“It will be a very ‘hot’ evening for Chelsea but I am really looking forward to it. These are the kind of games you want to be involved in. 

“We are happy to be back playing in the Champions League but this will will be our toughest fixture of the season so far.”

Given his love affair with Atletico, Courtois knows what lies in store for Chelsea better than anyone.