According to The Journal, Toon scouts watched Krul's fellow countryman Jeroen Zoet during PSV Eindhoven's 2-2 draw against FC Twente over the weekend.
The Magpies are also keeping tabs on Reading's Alex McCarthy and Watford's Jonathan Bond, the newspaper claims.
Alan Pardew realises that the club is vulnerable to bids for first choice keeper Krul, and his number two Rob Elliot. Krul, contracted to the club until 2017, has previously been linked with Arsenal and Barcelona. Irishman Elliot has been a loyal deputy, but there are concerns that he may seek a move away to secure first team football.
Newcastle reportedly made several enquiries for 22-year-old Zoet in the summer transfer window, but failed to reach an agreement with PSV. They were also unsuccessful with a deadline day bid for England under-21 star Bond.
On the striking front, the Magpies are believed to be monitoring the situation of CSKA Moscow frontman Seydou Doumbia.
According to Russian paper Izvestia, Newcastle and Everton lead the chasing pack, with German and other Russian clubs also keeping tabs on the 25-year-old.
Ivory Coast international Doumbia has scored 57 goals in 88 appearances for CSKA, with the Russian club likely to demand a fee in the region of £20 million.
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