The Mirror says Marin has failed to impress since joining the Blues from Werder Bremen last summer and will jump at a return to the Bundesliga so he can start playing regularly again.
The Stamford Bridge outfit are encouraging Leverkusen's interest in Marin, as they would like to finally land German international Schurrle at the end of this campaign.
Schurrle was a Chelsea target in the summer and a more recent inquiry was also rebuffed by Leverkusen, who are chasing a Champions League place.
However, the Germans will be powerless regarding Schurrle's future come the summer, when his 'fixed price' clause of around £25million kicks in.
Chelsea are expected to be in the hunt for the versatile Schurrle again at that stage - and loaning Marin to Leverkusen could lead to a part-exchange deal, or at least be viewed as a gesture of goodwill with an eye to close-season negotiations.