DeAndre Yedlin is facing five weeks on the sidelines with a thigh injury.
Ciaran Clark was forced off against Fulham last weekend with a knee problem, while Paul Dummett has been playing with a heel problem.
Jamie Sterry, meanwhile, has undergone surgery on his groin.
Wales manager Chris Coleman yesterday revealed that Dummett’s heel problem was a factor in his non-selection for a World Cup qualifier against the Republic of Ireland.
“He’s got a problem with his heel,” said Coleman. “He’s played with an injection with his heel (and) might need another. He needs a rest.
“If we were bare defensively, we would have called Newcastle, but we don’t need to do that.”
Dummett, however, could again play through the pain barrier for the Championship leaders against Birmingham tomorrow.
Yedlin suffered his injury in the win over Brighton and Hove Albion late last month.
The right-back has been in the United States to see his country’s team doctors ahead of international fixtures against Honduras and Panama. And the news out of Los Angeles has not been positive.
USA head coach Bruce Arena said: “DeAndre has been in LA this past week and examined by our team doctors.
“It is likely he will be out for about five weeks.
“I would expect he will be back on the field for Newcastle right at the end of this season in April.”