Newcastle are reported to have been given permission to speak to the player despite no fee being agreed with the Dutch club, who are keen to sell rather than lose him for nothing at the end of his contract in 12 months time.
"We never discuss transfer business with the media but, when we sign a player, we'll let you know," said Sir Bobby.
"We will let the press know if we move some players out or get some in."
Similar statements from Sir Bobby preceded the signings of Jonathan Woodgate and Hugo Viana.