The former Bayern Munich striker has been amazed by the progress of the France international who joined on loan from Juventus in the summer.
Coman, 19, signed a deal that will keep him at the Allianz Arena until 2017 but the Bundesliga leaders have the option to make his move a permanent one before his loan expires and Elber insists the club would be crazy to pass up that opportunity.
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He told Goal: "This guy is insanely good. It's incredible what he has shown at just 19.
"[When he came to Bayern] you thought he will be another substitute who can play if somebody is injured. But Coman distinguished himself from the beginning and showed good performances.
"For a coach it is very difficult to put somebody like him on the bench. And it would not make sense either. If you have the opportunity you have to buy him."
Bayern will need to stump up €21 million (£16m) to sign Coman permanently, though the teenager's agent, Francois Gil, has told Goal that talks over his future have yet to take place.