Sean Dyche has said that Murillo is struggling with illness ahead of Nottingham Forest's trip to face Everton on Saturday.
Forest got back to winning ways on Wednesday with a 1-0 win at Wolves, despite Dyche remaining without six first-team stars.
Dyche had hoped to have Murillo available for the Reds' trip to Molineux, but the Brazilian defender was not in the squad.
With Forest now preparing for a trip to Hill Dickinson Stadium to face Everton on Saturday, Dyche says he is being assessed on a daily basis.
Chris Wood
A few weeks ago, Dyche had pencilled in Forest's game against Leeds United as a possible return date for Wood, but four games on from then, there is no sign of the New Zealand striker.
Speaking on Thursday, Dyche revealed that the 33-year-old is in the early stages of his recovery.
"Chris Wood is making a bit of progress, but it's still early days yet," Dyche said.
Dyche confirmed that Murillo missed Wednesday's win over Wolves due to illness and that he is being assessed day-to-day ahead of the Everton trip.
"It was touch and go with a hamstring, and then he's been ill since, so we're just monitoring it daily," he confirmed.
"He's been ill since [the hamstring issue], so we're just hoping he recovers quickly."
Morgan Gibbs-White
Morgan Gibbs-White started against his former club, having suffered with a lingering back issue in recent weeks, but took some heavy knocks, which concerned some fans.
Dyche was quick to alleviate fears, however, insisting that he thinks the England international will be okay.
"I think he's alright," he said. "He took a few knocks in the middle; he's played a lot as you know.
"I don't think it's anything serious, or at least it's not been reported to me as anything serious, so just a recovery day today."
Dilane Bakwa
Dilane Bakwa played 61 minutes for Nottingham Forest B, in their 1-1 draw with Benfica on Wednesday.
Dyche offered a positive update but insisted the club are taking a cautious approach to his return.
"Dilane Bakwa played 60 minutes, so that's good," he said. "He came through that unscathed, but obviously we're taking it gently as he gets back match fit."
Douglas Luiz
Douglas Luiz is not yet training with Forest, but Dyche has revealed that he is close to doing so in his return from a hamstring issue.
"Douglas Luiz is close to getting back training with us," he said.
Ola Aina is not registered in Forest's Premier League or Europa League squad, so he cannot play until January at the earliest, but Dyche confirmed that he is not close to an imminent return anyway.
"Ola will still be a bit of time yet," he admitted.
Oleksandr Zinchenko
It was better news for on-loan defender Oleksandr Zinchenko, who Dyche confirmed is training with the first team.
"Oleksandr Zinchenko is on the grass and is doing fine, so that's good, he's on his way back."