The midfielder was not involved as Newcastle thrashed Chelsea 4-1 at St James’ Park in the Premier League on Saturday.
Howe is having to deal with a number of injuries to first team players at present and has seen his options stretched thin as a result.
Now he will have to make do without Willock for a period of time, confirming that the midfielder has an Achilles injury and the club will speak to specialists to determine the best course of action.
“It’s a recurrence of his Achilles injury”, Howe said via the Daily Mail post match.
“It’s a massive blow.
“We don’t know how long he’ll be out. We will seek specialist advice.”
Newcastle are now heading into a hectic period of games as the Christmas fixture list approaches and Howe will have to juggle his resources.
The Magpies are expected to look to make signings in the approaching January transfer window.
