Greg Taylor has limped out of today's Rangers vs Celtic showdown at Ibrox.
The full-back was replaced on the 20-minute mark by Josip Juranovic as he went down without being challenged.
Just yesterday Taylor was passed fit for the clash by manager Ange Postecoglou, but his hamstring knock appears to have flared up.
Juranovic, who has just returned from the World Cup, slotted in at left-back, while Canadian international Alistair Johnston started on the right.
On the decision to hand Johnston his debut, Postecoglou told Sky Sports: "It is a combination of things. He [Johnston] has been with us for a couple of weeks and he has trained well.
He is fit and ready to go. Jura [Juranovic] still does not feel 100 per cent so we went with Alistair in the end and Juranovic is available if we need him."
The Australian also detailed his reasoning for starting James Forrest in the derby match and that there has been a bug going around the Parkhead squad.
"There has been a whole range of things coming into the game," he continued.
"We have had a bit of a bug running around the team so there are a couple missing today who are a bit under the weather.
"With James I just think he has been playing really well lately and with most of these things players are in form.
"You put him in there and I know what he can do."
