The attacking midfielder joined the Premier League side in July 2012 after an injury-hit third and final season with Werder Bremen in the Bundesliga but the 24-year-old's debut year at Stamford Bridge did not go to plan as further fitness problems hampered his progress.
The Germany international started only two games in the league and, although he did pick up a Europa League winner's medal, it was a largely unsuccessful year for a player once dubbed the 'German Messi'.
In an attempt to help his international chances, Marin sought more playing time and joined Sevilla on loan for the season where, despite having more fitness issues, he has impressed - but he is uncertain of whether he will be able to return to the Blues.
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"My first year at Chelsea, I did not play a lot or have many opportunities and I wanted to play again and that's why I left for a year.
"At the beginning of the season [2012-13, with Chelsea] I got an injury and it was difficult to come back and then the manager changed.
"With [Rafael] Benitez I came on sometimes but I didn't start many games. I only played a few times so you can't judge how I did at Chelsea, as it was too short.
"It was very easy to settle in here in Sevilla," Marin added of his time away. "I feel very good here. Everything has been fine. The stadium is nice, the fans [too]. The team is very good as well.
"The beginning was great but I was unlucky with an injury. Now it is better again and I'm looking forward to playing in the second half of the season.
"I'm very happy here but I love London."
Sevilla have earned a reputation of selling academy products for big money such as Jose Antonio Reyes, Sergio Ramos and Jesus Navas, and Marin believes that they have another gem on their hands in Alberto Moreno, a target for Manchester City.
"We have a very good squad here with a lot of good young players," he enthused, "but I would say Alberto Moreno is one of the players who stands out in his age and position. He is very quick, young and I think he will have a great career."