Neil Lennon's fears were justified as Celtic lost to Livingston for the first time in a 2-0 defeat at the Tony Macaroni Arena.
The Hoops boss had warned of a "dangerous" Ladbrokes Premiership fixture at his pre-match press conference which proved to be the case after Parkhead attacker Ryan Christie was given a straight red card by referee Willie Collum in the 26th minute for a reckless challenge on Scott Robinson.
The Livi midfielder fired the West Lothian side ahead two minutes after the restart and striker Lyndon Dykes added a second in the 73rd minute to cement the Lions' first victory over the Parkhead club since they were renamed and relocated in 1995 after being known as Meadowbank Thistle.
It was Celtic's first defeat in eight league games, their winning run ended with a 1-1 draw at Hibernian last week, and Lennon said: "You can't panic but I am expecting better.
"I did tell them before the game that the fixture was a concern. It's a dangerous opponent in a dangerous environment.
"I knew Livi would be well up for it and they were. We needed to match that.
"It is a poor result. I thought we started the game OK, we were quite bright but obviously we lose Ryan very early and we have to adjust.
"We are OK going in at half-time, I thought we could go on and win it but it was really passive for the first goal and again we tried to force the issue.
"We were fine with 10 men without working the keeper enough and the second goal was really poor, we should be dealing with that."
The former Celtic captain had "no issue" with Christie's dismissal which left the Hoops a man down for the majority of the game.
He said: "It is totally unlike him but he is late. It maybe looked worse in slow motion but it is a red card.
"I am not happy about it obviously but it is not like him."
Livi boss Gary Holt welcomed the latest achievement by the West Lothian club.
The former Celtic midfielder, who watched his side win for the first time in five matches, said: "These things are there to be broken.
"We did it last year with the points we got and the clean sheets and the goals we scored. It's another tick in the box. I'm over the moon to be honest.
"I actually thought we played better against 11. We were right at it, I thought it was a really good game and then we got a bit disjointed because we had the extra man but there were gaps.
"We spoke to them at half-time about being patient and working the areas that we can, could we go around them. Playing against 10 men it's always hard to go through.
"I thought the first goal was great. A great bit of skill. Great movement, great pass, great finish. I think the game deserved that."