Tony Pulis says that two of his defenders remain sidelined for the trip to Birmingham City this Saturday (3pm).
The Boro boss admitted his concerns over his backline before last weekend's FA Cup win over Peterborough, and while he may have a few more options at his disposal tomorrow, Aden Flint and former Blue Ryan Shotton won't make the matchday squad.
"Flinty won't play, Shotton won't play - that's about it I think," Pulis said.
"It's a blow because this two have been important for us.
"But having said that Danny Batth will come n, and Dael [Fry] will come in, and they've done well for us as well. Dael has a big future at this football club."
Pulis says that the FA Cup tie was a good opportunity for fringe players and new signing Rajiv van La Parra to get much-needed minutes.
"I think looking at last week's game, Rudy [Gestede] still needs game time. One or two who played against Peterborough need that to get up to speed.
"But generally the lads have worked very well this week.
"Rajiv [van La Parra] has looked better and a lot sharper the week.
"But he still needs time, he's not played since October.
"He's a good lad, and he wants to be out on the training ground all the time, he's mixed in well with the lads. We know he's capable but at the moment we'll have to use him more as a game-changer than a starter.
"We understood that when we signed him."