Fabricio Coloccini's agent, Marcelo Lombilla, has accused Newcastle of hampering their chances of cashing in on the defender.
The Argentine moved for around £10million from Deportivo La Coruna last summer but failed to live up to his billing as the Magpies dropped down to the Championship.
Despite a season of irregular form, the 27-year-old is still highly regarded in Spain and is thought to be attracting strong interest from Real Zaragoza.
However, any potential move to suit all parties involved is being disrupted by Newcastle's reluctance to talk business as club owner Mike Ashley awaits a buyer, much to Lombilla's dismay.
"For weeks now, I only hear silence from Newcastle," Lombilla told The Chronicle.
"After the relegation, the directors seemed to decide to sell Fabricio. But I have heard no more details.
"Now, without more information, the chances to sell him look negative."
The Argentine international is also being tracked by Sevilla and Italian duo Lazio and Fiorentina, but Lombilla insists only Zaragoza have approached him.
"I have spoken with them, but without knowing Newcastle's position, it's nearly impossible to do a deal," warned Lombilla.
The lack of communication threatens to devalue Coloccini's worth with clubs now reportedly only willing to pay around £4million for his services, while others would prefer a loan deal.