The former Bristol Rovers winger is out for six months after suffering a serious injury late on at Bournemouth last weekend and will undergo surgery to repair a torn anterior cruciate next week.
His absence will give the likes of Kei Kamara, Emmanuel Ledesma and Luke Williams – who recently returned from an impressive loan spell at neighbours Hartlepool United – the chance to cement a first-team spot, with one player’s unfortunate loss another one’s opportunity.
Head coach Karanka said: “We have one less player now. We have other players and I’m happy with all of them. We have 10 games to go until the end of the season, we fight together.
“We have one player less but we need to be compact, we need to work hard and we need to carry on as we did before.
“For Muzzy, it’s horrible. But you can never rush back from an injury like that.
“He has to be strong, the most important thing is for him to be comfortable, he has to concentrate on his rehab and he will be back.
“He needs now to recover well and I am sure he will come back stronger and more mature, the same way like Rhys Williams will from his injury.
“He’s strong, he’s ready to start his rehab and the best way to show our support is to win on Saturday.”
Former Leeds United defender Jonathan Woodgate is fit again for the Teessiders following a calf problem.
But the veteran centre-half may have to bide his time and wait for a return to the starting line-up with young defenders Ben Gibson and Chelsea loanee Kenneth Omeruo having caught the eye in his absence.