The Fir Park manager admits he struggled to get out of bed in the days that followed Saturday's last-gasp 1-0 defeat to local rivals Albion Rovers.
But the former Scotland midfielder says the fatal incident in nearby Glasgow which saw nine people lose their lives when a police helicopter crashed into the Clutha pub has put his troubles into perspective.
McCall said: "As proud and as happy as I was a few seasons ago when we managed to get to a Scottish Cup final for the first time in 20-odd years, it was nothing compared to how low I felt after last Saturday.
"We had a youth-team game the next day that I went to and to be honest, I'd have rather stayed in bed because I didn't want to face folk.
"But you have to put things in perspective. It was a horrendous result but you look at the terribly sad news that came out on Friday from Glasgow, then it doesn't compare. No one died at the game and we have got to move on."
Well looked set to take the fourth-round tie to a replay when Gary Phillips struck in the final minute to secure a famous win for the Steelmen's Lanarkshire neighbours.
McCall admitted Motherwell contributed to their own downfall but has now challenged his team to respond by beating Scottish Premiership champions Celtic when they host the Hoops on Friday night.
"I remember being a young boy as a Leeds fan and watching as we got beat by Colchester. I also remember Newcastle getting beat by Hereford, York City going to Old Trafford and beating Manchester United.
"Even this season, Morton went to Celtic Park and won after 120 minutes to record a real upset.
"So these things happen. We were not good enough. We didn't have enough people going past their opponents in one-on-one situations.
"We didn't deserve to lose the game but we certainly didn't deserve to win it. It looked like a 0-0 all over but you leave yourself open to a sucker punch.
"It's one of the worst results we've had as a club and one of the worst since I've been a manager. But it's about how you bounce back."
While the Steelmen were the biggest scalp to be claimed so far, Celtic were busy tearing shreds off a hapless Hearts side, cantering to a 7-0 triumph.
But McCall thinks his side - who have beaten the Parkhead side on their last two visits to Fir Park - can compete with Neil Lennon's side.
"If you look at their performance last week and ours, then everyone will expect Celtic to come out and roll us over," he said.
"I watched that Celtic game at Tynecastle back and they were magnificent. But I have also looked back at the tapes of last two matches we played here and managed to get two victories. We can do it.
"However, we know we have to go at it from the first whistle and make it a right game if we are to win a third match."
Meanwhile, McCall says he has no knowledge of reports that defender Shaun Hutchinson has turned down a new contract offer.
He said: "It was news to me. This week hasn't been the right time to speak to Shaun. We will do that next week. But hand on heart, we haven't even made him an offer to turn down.
"Whether Shaun or someone else on his behalf has said he won't be signing on again, I'm not sure but it certainly hasn't said it to me."