Amini, 17, spent more than a week on trial with Dortmund where he impressed first-team manager Juergen Klopp.

It is understood Dortmund made an attractive long-term contract offer to Amini but the teenage midfielder is contracted with the Mariners for another year meaning the Germans must negotiate a transfer fee.

Central Coast owner Peter Turnbull told the Sydney Morning Herald that Dortmund had made an initial offer for Amini but said it was disappointing and needed to be increased.

"We've rejected their offer, and it wasn't that hard to be honest," Turnbull said.

"I can't give figures, but let's just say it was disappointing given Mustafa is probably one of the best young players we've seen in this country for a long, long, time.

“I talked it over with both our football department, and the FFA coaching staff, and everyone agrees his development at this stage would be best served by staying with the Mariners.

“He's going to the World Youth Championships in July, and he's already part of our first team, so there's a lot to look forward to."

Last year Dortmund were forced to make three bids for Melbourne Victory's Australian goalkeeper Mitchell Langerak before securing his services.

AIS product Amini made 23 appearances for the Mariners last term, scoring one goal.