Barnes, signed from Leicester in July for £38m, has had a scan and is waiting to see if surgery is required.

"It's an injury to a part of the foot just below the toe. I think it's quite a substantial injury," Howe said.

"I won't go too technical because I'm not qualified to do so but yes it's a very unusual injury."

Barnes, who has one England cap, has made seven appearances for Newcastle, scoring once.

Howe, whose side face Manchester City in the Carabao Cup on Wednesday, added: "He was down after the game because he knew it wasn't a normal injury where you feel a muscle and think that might be one or two weeks. This was a slightly more complex issue."