Kieran Tierney has suffered a setback in his bid to be fit for Sunday's derby.
The Celtic full-back has suffered a reaction to the calf injury which saw him miss Scotland's double header with Kazakhstan and San Marino.
Tierney flew back early from international duty to receive treatment in a desperate bid to be fit for the Rangers showdown.
And while he looked to be winning his fight for fitness, the 21-year-old has suffered a setback.
Neil Lennon confirmed Tierney will be assessed ahead of the crucial match which, should Celtic win, will go a long way to clinching 8-in-a-row.
Lennon said: "Kieran has had a bit of a reaction today and may be a doubt. We will have to assess him tomorrow.
"It is the same issue and we will leave it maybe as late as possible to see how it is.
"He looked uncomfortable so we will give it 24 hours to see how it goes."
