The winger joined Werder Bremen from Borussia Monchengladbach in 2009. While Marin performed well during the first two years at his new club, his form has dipped with the sale of Mesut Ozil to Real Madrid.
Allofs expressed his disappointment that the German failed to live up to the club's expectations. As such, when Marin refused a contract extension, the decision made to let him go was an easy one.
"Marko's development was not what we had imagined. He has his strengths, but they are not the ones we need at the moment. An extension was not an issue as he indicated to us," he shared with Bild.
The midfielder signed for Chelsea in a deal estimated to be worth 8 million Euros, and Allofs indicated a Blues player could be moving the other way.
"Chelsea have other plans, but I will not rule out another player coming to us."
Marin's Bremen team-mates had mixed reactions with regards to his departure to England. While central defender Naldo believes he would pose a threat to Premier League defences, midfielder Sebastian Prodl was not as optimistic about the German's impact.
"Marko is always dangerous with his dribbling. This may work well for him in England." Naldo stated.
"Chelsea will have something to think about, he won't grow any more. And he cost €10 million. He lacks strength, but he is nimble enough to compete against physically strong defences." Prodl said.
Werder Bremen host Schalke for their Bundesliga fixture this Saturday.