Dundee United defender Callum Morris faces a race against time to make the Celtic triple-header.
The centre half failed to reappear for the second half against Kilmarnock at Rugby Park on Saturday after tearing a thigh muscle during the first period.
His absence proved costly to the Tangerines as their rejigged defence failed to cope with an improved home team and lost an injury-time goal to lose 3-2.
Morris will now be sidelined for between a fortnight and three weeks, according to assistant manager Simon Donnelly.
That means the time frame is a tight one for the former Dunfermline man, with United playing the first of their three successive matches against the Hoops on March 8 – the Scottish Cup quarter-final at home – before the League Cup final at Hampden a week later and then the Premiership clash at Celtic Park on the 21st.
“Callum has hurt his thigh and he looks like being out for two or three weeks,” said Donnelly.
“It is a muscle tear and when there is damage there it is kind of hard to play through that and he could have caused more damage had he not come off at half-time.
“Hopefully, we have caught it quickly enough that he doesn’t miss the cup games.
“We will assess it over the next couple of days to see how it settles down but I spoke to him on Sunday and he said it was still sore.
“That’s the way it goes, I guess.
“The big guy has done fantastically well for us and played on with an Achilles problem before.
“He wanted to keep going on Saturday and that’s the type of character that he is.”
The loss of Morris meant United had to change their defence, with Ryan McGowan moving infield to join Sean Dillon and Euan Spark filling the vacancy at right-back.
With Jarek Fojut suspended that gave a really unfamiliar look to the backline but Donnelly still felt they should have been more resilient.
“We had Ryan and Paul coming in having not played many games,” said Donnelly.
“For example, Ryan is actually going through a mini pre-season with us.
“He is going to get better the fitter and stronger he gets and you can say the same about Paul.
“We had young Euan Spark coming on to do a job at right-back in the area where Kilmarnock arguably had their most dangerous players.
“But we had the lead at half-time and needed to be stronger.
“With their getting the goal just into the second half our shape and discipline went and we need to address that for the St Johnstone game.
“We now have four games back-to-back at Tannadice and our form at home has been decent.”
Donnelly stressed that blame for the defeat at Kilmarnock – their second of the season at the Ayrshire venue – should not be put on goalkeeper Rado Cierzniak,
Cierzniak certainly should have done better at Killie’s first two goals but Donnelly wasn’t keen to single out one man for criticism.
He said: “I haven’t spoken to Rado but if you ask anyone involved in the team from us right down to the boys who played at Kilmarnock the second half was one to forget.
“You can pick out individual mistakes but we win and lose as a team.
“I think to direct everything at Rado would be very unfair.”
Donnelly did admit that the management have been left extremely frustrated by the players’ ability to look both excellent and poor within the same match.
“The real disappointment for us was that we went from a first-half performance in which we looked likely to score every time we went up the park to a second half in which we struggled and didn’t really create a chance,” said the Tannadice assistant boss.
“We had been on a decent wee run and we wanted to gather momentum.
“You look to Aberdeen and see how they have continued to get good results and we wanted to have that.
“People have criticised our (lack of) consistency and that second-half performance kind of loads the gun a bit for them.
“So we need to work on it.
“Nobody likes criticism if it’s constructive then fair enough and maybe criticism in the past regarding consistency has been a wee bit harsh at times.
“However, it has been really frustrating and confusing for us because we seem to be making progress and everything is going well and then we let ourselves down for 45 minutes and that knocks us back three or four steps.
“The good thing is that this season when we have had a setback we have bounced back quickly and hopefully that will happen on Saturday against St Johnstone.
“But when you get a second half like that then you can’t put up much of a defence against it.
“It wasn’t good enough.”