Sam McQueen is facing a lengthy spell on the sidelines after sustaining a serious knee injury in the Carabao Cup victory over Crystal Palace.
The versatile wing man went down in some discomfort just 30 minutes into the game after attempting to cut out a cross from Palace winger Andros Townsend.
The Southampton loanee was stretchered off the pitch, being replaced by fellow summer signing George Saville.
“Sam’s news is not good,” Pulis told the media during Friday’s press conference.
“He’s done his cruciate so I don’t think we’ll have him for a very long time.
“We’re talking to Southampton now to see if he’ll stay here to recover or if he’ll return to his mother club.
“It’s a real disappointment because Sam’s not had the opportunities he would have liked, but he is a great character and he has been fantastic in the dressing room.”
Elsewhere, right-back Ryan Shotton remains unavailable for selection through injury.
Centre half Daniel Ayala is suspended after accumulating five yellow cards.
To add to Boro’s woes, the squad has been hit with a sickness bug and Pulis’s team selection for Saturday much depends on the well-being of the players.
“With the bug we had earlier in the week, the doctor has had a few in earlier today to see how they are,” he said.
“We’ll go through that and we’ll pick the team from there.
“There will be a few changes, because of injuries and suspension.
“The ones we call on we want them to go out there and give it their best.”