The midfielder has struggled for game time this season, playing one one game so far this term.
McClaren, the former England manager, is advising Derby's board, and recommended Longstaff's signing on loan.
But former England goalkeeper Paul Robinson does not think Newcastle can let him go, given the COVID-19 outbreak at the club.
He told Football Insider: "He has not been playing, he has barely sniff at all but now is his chance.
"Steve Bruce cannot afford to let any of his squad go with the current coronavirus situation. The positive tests may have thrown the January transfer plans into chaos.
"Players that could have left may now be told that they have to stay.
"If he was allowed to leave on loan it would be similar to Troy Parrott.
"Get out to a top Championship club, get playing and show people what you can do.
"I think he would come back a better player if that happened."