Barnes, who signed from Leicester City in July, was forced off with the injury in the 12th minute of Newcastle's 8-0 win at Sheffield United on Sunday.

"I think it's an injury to a part of the foot, just below the toe. I think it's quite a substantial injury," Howe told reporters ahead of Newcastle's League Cup game against Manchester City.

"We've had it scanned, we're waiting now for the specialist's opinion on what to do next, whether there is surgery involved or not," he added.

"I don't think it was a tackle, just pushing off to run, a very unusual injury."

Anthony Gordon replaced Barnes in the thumping of Sheffield United, and was one of eight different scorers in that game. His manager was full of praise for the 22-year-old.

"He's had an outstanding start to the season. What's pleased me most is his fitness level, his athleticism has really come to the fore," Howe said.

"He's added goals, end product, he had an assist and a goal on Sunday which is great to see."

Gordon joined Newcastle in January from Everton, but struggled to force his way into the side making just four appearances in the starting team. The midfielder already has five starts this season.

"Sometimes there's a bedding-in period, some players take longer than others," Howe added.

"We had no doubt about Anthony's quality, but I think pre-season did him really good, as did the six months with us before the summer break."

Newcastle, who lost to Manchester United in last season's League Cup final, host Manchester City in the third round of the competition on Wednesday.

"It's an important competition for us. We will give it every importance, we will try as hard as we can to progress because we want to try to compete in every competition," said Howe.