The duo both missed Saturday's 2-0 win at home to Bristol City for which 20-year-old Will Huffer made his Whites debut in goal with fellow 'keeper and former loanee Jamal Blackman back at parent club Chelsea having broken his leg.
Peacock-Farrell is now back available but Jansson remains sidelined with Whites head coach Marcelo Bielsa unsure if the Swedish centre-back will be back for Saturday's clash against Sheffield United at Bramall Lane.
"Jansson won't be available and Bailey can be a starter tomorrow," said Bielsa, asked about his latest team news.
Asked when Jansson would return, the head coach said: "At the beginning, he was supposed to be available for last Saturday and then tomorrow but it was not the case and that's why I would like to be cautious before saying he can play next Saturday."
Bielsa also revealed that centre-back Liam Cooper is fine after receiving treatment to his knee during the second half of Saturday's win against Bristol City.
"He is fine," said Bielsa.
With Jansson sidelined, 20-year-old Finn Aapo Halme made his Whites debut against the Robins as part of a back three alongside Cooper and Kalvin Phillips.