The Magpies are desperate to secure some new faces before they head off to New Zealand on Friday for their pre-season tour.
However, as with France midfielder Remy Cabella, Janmaat would not travel Down Under due to his particpation in the World Cup finals with Holland.
Arsenal boss Arsene Wenger has already signed Alexis Sanchez but has been forced to wait to finalise a deal for defender Debuchy with Newcastle holding off as they search a replacement.
And, according to Sky sources, it appears the delay for Wenger could be over with officials at Newcastle and Feyenoord continuing discussions over the Dutch right-back.
Newcastle have now agreed a deal for Janmaat and the player is expected to have his medical on Tyneside on Tuesday.
The St James' Park club are also hoping to secure the acquisition of Monaco striker Emmanuel Riviere for a reported fee of £6m.