AS understand the Magpies are among the list of suitors for the 20-year-old Ghanian, who has a release clause £9.5million.
Ole Gunnar Solskjaer’s Red Devils are said to have already approached the La Liga club but the player’s agent remains attentive to all options for the summer.
Interestingly, Salisu’s agent is believed to be the father of Juan Mata, so that may have an impact on future negotiations.
Real Madrid, Atletico Madrid and Valencia are also credited with interest. He has made 23 appearances this season.
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Meanwhile, Magpies under-23s captain Oliver Walters believes tonight's derby at St James's Park is the youngsters' biggest game of the season.
The Tyne-Wear rivals face off in Premier League 2 with the Black Cats rooted to the bottom of the table with just one point, compared to Newcastle's 19.
He told NUFC.co.uk: "I'd say playing against Sunderland at St. James' Park is probably our biggest game of the season.
"Other than if we managed to get to a final in other competitions, this is definitely the biggest game for us in the league.
"We don't want their first win to be against us. In a derby game, anything can happen so we need to be really focussed.
“If we focus and do what we have been doing recently, then the result should take care of itself”
He added: "Being captain for the team has been great too. I've been loving it, really. The results have been good for us and it's been really positive. If everything goes well, we can come out on top.
"Since under-nine level, I've played against Sunderland and it's always a big game and a one you really want to win with them being your local rivals. It does means a lot more.
"A lot of the lads have been here for years and years. They've played Sunderland since a young age and we tend to have a good record against them so we'll be hoping to keep that going."