The Magpies formally confirmed de Jong's arrival yesterday, with a view to a permanent £8m transfer in the summer, and are also hoping to recruit French midfielder Clement Grenier before the transfer window closes tomorrow night.
Newcastle officials tabled a bid of around £8m for Grenier yesterday morning, but it was swiftly rejected with Lyon holding out for at least £12m before they will even countenance a sale.
Further talks are planned later today, but de Jong's arrival at least means Alan Pardew has greater attacking resources at his disposal in the second half of the season.
The Holland international, who has been registered in time for Saturday's Tyne-Wear derby with Sunderland, was a major part of the FC Twente side that won the Eridivisie title in 2010.
However, his career has stalled since he moved to German club Borussia Monchengladbach for 15m Euros in the summer of 2012, and he moves to Tyneside having not scored a senior goal since March.
“This season hasn't been that great for me,” said de Jong. “There have been ups and downs, some good moments and of course some bad. But it's always difficult in your first season away from Holland.
“I hope I can play here. I feel good and feel fit, so that is not a problem. I'm really happy to be here. It's great because the club has been looking at me for a few years now and now I am here it is good.”
De Jong will train with his new team-mates for the first time this morning, and with Loic Remy suspended, will go straight into the squad for Saturday's derby with Sunderland.
Whether he starts ahead of Shola Ameobi remains to be seen, but his prior knowledge of a number of his team-mates should enable him to settle in reasonably quickly.
“I know Tim (Krul) really well from the national team and he's a good friend,” said de Jong. “I have seen Vurnon (Anita) a few times in the national team and I also know Cheik (Tiote) from our time at Twente together.
“I spoke with Tim a lot about what the club was like and how they play football. I have watched a lot of their games in the Premier League because it's a great league. Tim told me a lot about the club.”
While de Jong was being confirmed as a Newcastle player, Yohan Cabaye was attending a press conference at Paris St Germain, and with the midfielder's £20m move having been completed, Newcastle officials made a renewed approach to Lyon in an attempt to sign Grenier.
The Magpies discussed a potential fee of around £8m yesterday morning, but that still leaves them a considerable way short of Lyon’s valuation of the 23-year-old France international, who has scored 12 goals in 89 senior appearances for the Ligue 1 club.
Lyon owner Jean-Michel Aulas has briefed French sources that he is unwilling to accept less than £12m for Grenier, and is minded to hold out for £15m in order to secure a ‘January premium’ for the disruption caused by selling a key asset halfway through the season.
Mike Ashley’s willingness to pay the whole of a transfer fee up front has proved a useful bargaining tool in similar negotiations in the past, but while further talks are planned, an agreement remains some way off at the moment.
“We have players who have been asked to go,” confirmed Aulas. “We have had a proposal for Clement Grenier. This is after the departure of a number of Newcastle players.”
Cabaye's departure has cast a long shadow over the final week of the transfer window, although Tuesday night's spirited display at Norwich City assuaged fears that the rest of the Newcastle squad would struggle to cope without the Frenchman.
While the Magpies were unable to make a breakthrough in the goalless draw at Carrow Road, their attacking play was effervescent throughout, with Hatem Ben Arfa effortlessly assuming the mantle of creator-in-chief.
Ben Arfa will be available to face Sunderland despite suffering from cramp in the latter stages of Tuesday's game, and while Remy's absence is another hurdle that will have to be overcome, there is a strong sense of purpose ahead of Newcastle's biggest game of the campaign.
“We have such a strong squad that, as we showed (on Tuesday), no matter who gets picked, they will perform,” said Steven Taylor, who is expected to retain his place in the back four alongside Mike Williamson. “Things happen in football – a player goes out and a player comes in.
“We responded very well (to Cabaye's departure) and that will keep everyone quiet. We knew if things didn't go for us, the press would have had a field day, but we put on a very good performance.
“We are pleased, and the manager is delighted with us. What we have to do now is go on and make sure we take those chances in the next game.”