Willock netted the opener for the Magpies in the Carabao Cup second round clash after just 18 seconds, but was later withdrawn at the City Ground where United progressed after winning the penalty shoot-out.
But speaking ahead of Sunday's Premier League visit of Tottenham Hotspur (kick-off 1:30pm BST), Howe revealed that an initial scan had brought "relatively good news" - but added a further scan would take place to fully determine the nature of the injury.
The United head coach also spoke about Kieran Trippier's international retirement and the challenge posed by Ange Postecoglou's Spurs this weekend. Here are some of the main topics up for discussion in Friday morning's media briefing:
On the extent of Willock's injury…
"Joe had a scan yesterday, an early scan. It is relatively good news.
"I don't think it is a serious injury, but it is early, so we will re-scan again in a few days again just to confirm that."
On Spurs…
"Tottenham have been very good - they continue to be a team I like to watch, a very attractive style, fluid. They have recruited well and signed some really talented players.
"They were good last year, but I think they will be even better this year. I think we always have entertaining games against them. For us, we need to make sure we get on top of the details."
On the start to the season…
"There are no easy games. We have done well to get four points so far as we have not been at our absolute best. Against Tottenham, we are going to have to be at our very best to get something from the game."
On Sandro Tonali, who made his long-awaited return to action in midweek…
"I was so pleased to see the support for Sandro. You could feel the warmth and the genuine love and affection.
"You can see the outpouring of love from Sandro to the fans at the end. He would have loved being back out there."
On Trippier's decision to retire from international football…
"We back it totally. It is a time for celebration, for what he has achieved with England. He's an outstanding player.
"I was really proud to see how he has taken his career to that level. He should be proud of everything he has done and look back fondly on those memories."
