For three years they've been waiting at Werder Bremen.
But now that potential could be realised at Chelsea after they struck a £6.5 million agreement for the 23 year-old. That he joined Werder for €8.5 million is a clear sign that Marin failed to meet expectations over his three years at the Weserstadion.
Even his Werder teammates were stunned by the news.
Chelsea are signing potential - even at 23 years of age.
Fast and boasting wonderful close control, Marin has shown at international level and in the Champions League he can win games on his own. But critics point to his lack of consistency, not just over a season, but throughout 90 minutes, and pick holes in his play.
His former Gladbach coach Hans Meyer was a regular critic of his poor defensive game and actually dropped Marin for a time to convince him to work harder off the ball.
"I'm not a defensive player," complained Marin. "It’s not my game - other players are stronger at this."
Others have spoken of Marin's dribbling. As exciting as he is on the ball, he has a reputation of running down cul-de-sacs, though this season he appears to be more focused when in possession.
It’s no coincidence he grew up modeling his game on Bayern Munich legend Mehmet Scholl.
"I wasn't a Bayern fan as a boy, but I was a fan of Mehmet Scholl. When I had the chance to play against him, I asked for his shirt before the game so I could get it before any of my teammates."
Marin was born to Bosnian Serb parents and moved to Germany as a two-year old.
He admits he owes his success to his family.
"They still play a big role. My mother used to drive me to every game, my father was doing it before then, even at away games in my youth.
"Every year we go back to Bosnia for holidays and my friends and family are always pleased to hear of my success. They watch me on television and keep press clippings of me. It's always sad having to leave them to come back."
Since the Chelsea move went public, German critics are questioning whether he can handle the physical side of the Premier League.
"I don't care about that. If my opponents try anything, I'll just be quicker. Anyway, it's only what Chelsea thinks that matters," he declared.
Marin confesses he's always had his heart set on moving to England. Indeed, it appeared he would be pulling on a Tottenham shirt earlier this season, with rumours of a London visit for a late January medical having to be denied by Werder.
Now Marin is focused on life with Chelsea and is convinced, after speaking with Blues football staff, their system will bring out the best in him.
"It fits me perfectly. I'm designed especially Chelsea, whose play is based on the wings. I'll see plenty of the ball.
"I'm not afraid. It's the perfect move for me."
While not a snip, at £6.5 million Chelsea obviously feel they can afford to take a gamble. So far, Marin has managed to produce in fits and starts. If he can rid himself of that inconsistency which has left past coaches so frustrated, then Chelsea will definitely have uncovered one of the great bargains for summer 2012.