The Fir Park manager was less than impressed by his side's 3-0 defeat at Ross County last time out, which followed a 1-0 home reverse at the hands of Dundee United.
McCall was without experienced defensive duo Stevie Hammell and Tom Hateley for the County calamity, while Fraser Kerr was ill, but the Well boss is hopeful at least two of that trio may be back in the frame.
McCall was also cagey over a more prominent role for former Scotland star James McFadden, who has come on as a substitute in his first two appearances since returning to the club last week.
But the Steelmen gaffer has left his troops in no doubt that a vast improvement will be required if the Lanarkshire men are to take anything from Neil Lennon's runaway leaders.
McCall said: "I am looking at the possibility of a shuffle, but that will depend on just who is available from the lads who missed out last weekend.
"We were very flat up in the Highlands, and there can certainly be no repeat of that against Celtic tonight.
"The bottom line is that things are so tight that the first thing we have to make sure of is our top-six place. We are just two points ahead of Hibs in sixth place and three in front of Kilmarnock and Aberdeen in seventh and eighth.
"Things could not be closer, but we have six games until the split, and we must treat these as six cup finals. Celtic come here in fine form, having just put five goals past Dundee but, at home the onus has to be on us to be positive no matter the opposition."
The Motherwell manager has taken encouragement from his side's last meeting with the Hoops when only a second-half Gary Hooper goal separated the sides.
McCall said: "I think Celtic have scored 23 goals in their five SPL home games since we played them at Parkhead at the beginning of January. So we can take a bit of encouragement from how competitive we were in that game.
"But I always believe it is vital you start well against either half of the Old Firm and at Parkhead in our last game with them, we managed to ride our luck a bit while also keeping a good defensive shape and really stayed with them.
"We need the same levels of application and focus tonight and, hopefully, if we can produce these, we can get something from the game. Then we have another tough game looming at Tynecastle with Hearts and it would be a major plus to be going into that one with a positive performance and result from tonight's game."
While McCall accepts McFadden is recovering his sharpness after two cameo roles off the bench, the Fir Park gaffer was playing it cute over the player's hopes of a first start tonight.
The Well boss said: "James' pedigree is well-documented, but he is like everyone else in the squad in that he is competing for a starting place.
"Over the years, though, it has been obvious that he has relished the big-game occasion and tonight is a huge match for us.
"At the same time, we need to make sure he is ready to start and able to sustain his performance levels if he does so.
"Therefore, that is another decision that will go into the selection mix ahead of tonight."