Middlesbrough will be without key defender and stand-in captain George Friend for a number of weeks after picking up an injury in training, Aitor Karanka has revealed.
However, Karanka has now stated that while he is not certain on the extent of the injury, the popular 29-year-old is likely to be out of action for a spell between three weeks and a month.
He could therefore miss vital relegation shoot-outs with Hull City, Burnley and Swansea City over the festive period.
Potential replacements for Friend
Summer signing Fabio da Silva is likely to continue in his absence, though Boro do have other options in the left-back position. Right-back Antonio Barragan could be moved over to the left flank, with either Calum Chambers moving to the right or a recall for last season's first-choice right-back Emilio Nsue.
Though club captain Grant Leadbitter is back to match fitness after a long spell on the sidelines, young defender Ben Gibson is likely to keep the captain's armband when his side visit Leicester City this weekend.
Whoever does take Friend's left-back position will likely have to deal with the threat of Riyad Mahrez and Marc Albrighton on the Leicester right, with the Foxes buoyed by their recent Champions League knock-out qualification.
Karanka has options in defence and midfield
Despite the Friend blow, there was good news elsewhere with the implication that centre-half Dani Ayala is back in contention to start after a frustrating niggling ankle injury.
Karanka stated in his pre-match press conference that "the rest [of the squad] are ready", leaving him with a wealth of options in the defensive third of the pitch.
He must choose between Chambers, Gibson, Ayala and Bernardo Espinosa as a centre-back pairing, while he also has a decision to make as to his central midfield.
It is unclear whether Boro will line up in their regular 4-2-3-1 formation or the 4-3-3 set-up which has seen an upturn in form in recent weeks.
Adam Forshaw, Marten de Roon and Adam Clayton have all staked their individual claims to start in the last few fixtures, but the late introduction of Leadbitter in the Chelsea defeat - preferred over striker Jordan Rhodes as an impact sub - could suggest that Karanka is keen to re-introduce his captain to the starting fold sooner rather than later.