The club agreed a half-season deal with Leicester City earlier today.
And Sky Sports broadcast footage of Slimani arriving at Newcastle International Airport on a private jet.
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Slimani will now undergo a medical before formally joining Newcastle on loan before tonight's 11pm transfer deadline/
The 29-year-old, signed from Sporting Lisbon for Â£28million in the summer of 2016, has a thigh injury which could sideline him for two weeks.
West Ham United had also been looking to sign the Algeria international, who has scored five league and cup goals for Leicester this season.
Newcastle secured Slimani after losing out on Liverpool's Daniel Sturridge, who joined West Bromwich Albion on loan earlier this week.
United also failed to meet Feyenoord's Â£20million valuation for Nicolai Jorgensen.
Speaking yesterday, manager Rafa Benitez said: "We’re trying to do things. There’s the way, there’s another way, but we are trying to do things and sometimes it depends on a phone call, a meeting and then one player is doing a deal, and that means they have to move another player.
“Sometimes it’s that. It’s not the ideal situation when you have been working for months, preparing names and analysing players and then you go to January 1 with a list of players.
“Then you start with the names, the main target that you have.
“And after you have to go to the 31st and are waiting for a phone call from someone else.
“It means that something is wrong. But we can’t change what’s going on here for a while. What I can try is to do my best now.”