United have scouted the big defender for the last 12 months and Alan Pardew has already said openly he wants a centre-back.
Douglas told the Evening Chronicle: "I have another season on my contract. But I am ready to take a step forward. For my style of play I would go to Germany or England.
"Many clubs have already probed me.
"Newcastle, Schalke and Borussia Dortmund plus one team from Russia. But at the moment I'm not talking to anyone."