A hint of cockiness, even complacency, may have seeped into the Major League Soccer club that is off to a surprise 4-0-0 start.
Schallibaum sensed a problem in practice and let his team know it with some harsh words.
The Impact have been finding ways to win and sit first in the 19-team league, but he didn't want any letdown heading into an away match Saturday against Sporting Kansas City.
"Sometimes you just do this," the 50-year-old said. "When everything's OK, the players maybe get a bit low.
"Everything is good, so we must be stronger than before."
The Impact will play their first game on a grass pitch this season against struggling Kansas City (1-1-2), which is coming off a scoreless draw at New England.
Montreal began its second MLS campaign with wins in Seattle and Portland, then posted wins over Toronto FC and the New York Red Bulls at Olympic Stadium for a perfect 12 points after four matches.
They have conceded only two goals and scored six.
And while they have mostly been outshot and have held possession less than their opponents, they have used clinical counterattacks to claim the lion's share of quality scoring chances in each game.
Schallibaum will not complain about that.
"It's better pressure than when you're behind and you need the points absolutely," Schalibaum said. "It's a nice situation.
"We are first. We are the team to beat. I like this more than another way. That's pressure also, of course, but better than any other situation."
Getting too sure of themselves is another matter, however.
"He's calling us out on it," said defender Jeb Brovsky. "It's a good voice to have in the locker room, saying that just because you're on top of the mountain it doesn't mean you won't get knocked off next week.
"Going into Kansas City, a tough game _ if you go into there with a big head it's easily deflated."
The Impact should have the same lineup that edged the Red Bulls 1-0 last weekend. Defender Alessandro Nesta is still nursing an injury, so 20-year-old Karl Ouimette of Terrebonne, Que., will make a second start at centre back alongside veteran Matteo Ferrari.
They have midfielder Sanna Nyassi back from national team duty with Gambia available as a substitute.
Striker Marco Di Vaio will be looking to score in a third straight game.
What Kansas City's lineup will look like is a guess.
Midfielder Graham Zusi and defender Matt Besler played for the U.S. national squad in a 0-0 draw in Mexico on Tuesday and it was uncertain if they will start. They are hoping right back Chance Myers can return after missing two games with a leg injury.
Sporting finished first in the Eastern Conference with an 18-7-9 record last season, but points have been hard to come by since they opened the season with a 3-1 win over Philadelphia.
The loss of scoring star Kai Kamara to Norwich City hurt, and they also have forwards Teal Bunbury and Jacob Peterson out with injuries. New Argentine signing Claudio Bieler leads the club with two goals.
Kansas City likes to bring its fullbacks into the attack and pressure opponents, especially at home. That may mean another game where Montreal's opponent has the ball most of the time. But it could also play into their ability to strike on counterattacks.
"They are a team where we have to be more conservative and do what we can to get three points," said Brovsky. "Kansas City is one of the toughest places to play for sure.
"They have so many guns up top. They don't have the results maybe they wanted so far, but it's a team that can punish you. If guys like Zusi get time and space, they can pick apart defences."
It will be another test for goalkeeper Troy Perkins, who has been solid from the start of the season.
His play this season put the 31-year-old American into the league's top-10 all-time in games started, minutes played and saves.
"I don't think it matters who they play, they play a high tempo, high pressure game," Perkins said of Kansas City. "That's their style.
"They're full of energy. They're at home and they come out flying."
That could be why Montreal's coach was concerned about taking opponents lightly.
"Some guys may be tuning out a bit on some drills that are supposed to be high-paced," said Brovsky. "Whether that's complacency or being on a high, I don't think it's gone to anybody's head.
"Everyone's confident and comfortable going forward, but I don't think it's cockiness."
The Impact won't play again until they move outdoors to Saputo Stadium to face the Columbus Crew on April 16. A match in Los Angeles scheduled for April 6 was postponed to October to let the Galaxy concentrate on CONCACAF Champions League play.