Nottingham Forest fans are anxiously awaiting updates on Murillo's condition ahead of Sunday's Premier League clash with Newcastle United at St James' Park.
The Brazilian defender lasted just 28 minutes of Thursday's 3-2 Europa League loss to FC Midtjylland due to injury, feared to be a thigh issue that could impact his participation in this one.
Ange Postecoglou had no further detail on Murillo's problem shortly after full time - only describing his concern as a "knock" - but the tight turnaround makes it difficult to envisage the centre-back featuring this weekend.
As a result, Postecoglou should revert to a four-man defence with Nikola Milenkovic and Morato protecting Matz Sels, while Nicolo Savona replaces Murillo in the rearguard.
The visitors are still missing Oleksandr Zinchenko (groin) and Ola Aina (thigh), so Savona is the next best thing in defence, where Neco Williams will reprise his familiar left-back role.
Further forward, midfield fulcrum Elliot Anderson is a shoo-in against his old team, but the need for fresh legs could see Nicolas Dominguez re-introduced over Ibrahim Sangare.
Postecoglou may also consider bringing the veteran Chris Wood back into the first XI after his clinical - but inconsequential - penalty in the loss to Midtjylland, as Igor Jesus makes way for the former Magpie.
Nottingham Forest possible starting lineup:
Sels; Savona, Morato, Milenkovic, Williams; Dominguez, Anderson; Ndoye, Gibbs-White, Hudson-Odoi; Wood
> Click here to see how Newcastle could line up for this game