Middlesbrough boss Tony Mowbray says Kevin Thomson was withdrawn from Tuesday's 2-0 defeat by Nottingham Forest as a precautionary measure.
The 27-year-old was forced off with a hamstring strain late in the game at the weekend, his seventh game back since recovering from an ankle injury.
"It got tight so he needed to come off or it could have been six to eight weeks," Mowbray told BBC Tees.
"The boy has suffered and hopefully by coming off it won't be so long."
Mowbray added: "It was a decision I made, I was going to take Kevin [Thomson] or Nicky [Bailey] off.
"I thought Kevin would have been at the stage where he could get through 90 minutes and push on in his fitness side of things but obviously the last six or seven minutes were a problem for him."
The Teessiders' squad was also stretched by the absence of captain Matthew Bates and utility man Rhys Williams, both of whom were ever-present in the Championship prior to the game.
"They're both injured. Rhys' really is an injury that has been coming the last few weeks. He's had two games for Australia in such a short space of time and has caused a problem for him," Mowbray continued.
"It's a strain problem that he suffered with for a long time last season. He was unavailable to play, too sore, and we need to rest him and give him a chance to play again soon.
"It's a concern. It's been there for a while. We've tried to manage him through and he's done exceptionally well.
"Generally he hasn't been asked to work too hard. He's used his brain and his quality in the position we've asked him to play, but he's gone away with the national team, ran up and down the wing incessantly and it's dragged a bit on the problem.
"Games come thick and fast in the Championship at the moment and it's a problem for him.
"Matthew's got a foot problem he's been carrying for a week or two. It's just too sore at the moment but hopefully it will be alright."