Gary McAllister admits Rangers will have to wait for the results of Scott Arfield's ankle scan before deciding if the midfielder is fit enough for Old Firm battle.
The Ibrox ace had to be replaced just six minutes after climbing off the bench during Saturday's win over Hibernian after being hurt in a collision with Melker Hallberg.
He will definitely be missing for Wednesday night's clash with St Mirren but Rangers assistant McAllister insists it is still too early to tell if the Canada international will also be ruled out as the Premiership leaders look to stretch their 16-point lead over rivals Celtic in Saturday's derby clash.
McAllister, speaking ahead of Gers' trip to Paisley, said: "It is obviously difficult to find a facility to get a scan for Scotty (because of the time of year) but he is en route as we speak. We're just waiting for the results to come back.
"It's quite rare to see Scotty lie down on a pitch and be carried off as he's generally very robust, so it was pretty disappointing to see him come off the pitch the way he did.
"But we're hopeful that the scan will show up better than how it first looked.
"We'll wait purely for the results of the scan (before deciding how long he will be out). That's the position we're in."
Gers are already without Ryan Jack due to a problematic knee injury which continues to frustrate boss Steven Gerrard.
But McAllister is confident the Light Blues have the squad strength to cope with another huge week which could go a long way to deciding their title fate.
He said: "As far as Jacko is concerned, we're just going to have to be a bit more patient with Ryan.
"We were a bit hopeful that he could have been in for the Hibs game but we just have to sit back and wait for him to get fully fit.
"It's been mentioned a few times that we have a big squad and I think that's what you need to meet the demands of the schedule that we have.
"We're not focusing on Europe at the moment but the league schedule is very fierce.
"This is where we have to utilise the squad and try to rotate things, while also being careful of not disrupting the rhythm that we're in at the minute because we're in a good place."
Rangers' only bump on an otherwise blemish-free campaign came just two weeks ago on their last visit to Paisley when Saints brought a 27-game unbeaten run to an end by dumping Gerrard's team out of the Betfred Cup.
They have bounced back with three straight wins over Motherwell, St Johnstone and Hibs – but McAllister admits the Ibrox men want revenge against the Buddies.
"It's only natural when a defeat is only a few days ago for a player to think, 'They turned us over, we need to get one back on them'," he said. "I think that's a natural instinct that any footballer should have.
"But we're aware that they're a team playing with a bit of confidence.
"However, we have to go there and make sure it's all about us. We've done all our due diligence on St Mirren, we know their strengths but we have to look at what we do on the day.
"If we go there and perform, if we execute, we hope we can get the right result.
"Our preparation is short because of the amount of games but we'll just be going into this game like the last three since that poor result in the cup – fully focused and looking to get the win.
"We're fully aware of the schedule and what fixtures are near but the big strength and what the players have shown is their focus on what's directly in front of them and the next game is St Mirren.
"Once we play that game we'll turn our attention to the next one but we're fully focused on going to St Mirren and getting the right result."
