Jamaal Lascelles left St James's Park on crutches after being forced off against Bournemouth.
Newcastle United's captain suffered an ankle injury in yesterday's 1-0 defeat to Eddie Howe's side.
Lascelles, replaced by Ciaran Clark, also wore a protective boot on his left foot as he left the stadium after the game.
The 23-year-old updated fans on Twitter last night.
"Disappointing result," said Lascelles. “Gutted I had to come off the pitch. Scan Monday, so hopefully not too bad. Thanks for the support.”
United manager Rafa Benitez had been without Mikel Merino for the Bournemouth game.
The midfielder could be sidelined until next month.