The Reds take on the Teessiders at 20:00 GMT on Friday night in the first of the Emirates FA Cup fourth-round ties taking place over the weekend.
There is positive news regarding Paul Pogba, who looks set to feature for the first time under Ralf after recovering from injury.
"Paul will be part of the group," confirmed Rangnick at his press conference to preview the tie. "He might even be in the starting XI.
"There are still a couple of players missing out. Edi Cavani will only return on the weekend. He contacted me a week ago and asked me if he could have two more days at home and I allowed him because I knew that he couldn't be in the starting XI anyway, with jet-lag and only coming back today or last night.