Sheffield Wednesday have won their last three games in all competitions.
The Owls have won their last three matches in all competition, and knocked Newcastle United out of the Capital One Cup during that time.
However, Carvalhal doesn't want his team to get carried away with their good run of form, and has reminded them on the training ground that they must be at their best if they want to get a result against Preston.
“This is a dangerous game,” he said. “When everyone expects one thing, sometimes people relax and there can be surprises.
“We are working with our players to put them on red alert for this game. Preston are a dangerous team and we must show the same team spirit we showed in the last couple of games.
“We are focusing the players and telling them to forget the past. The future is the most important.
“You can’t sleep in football because you can lose everything in one minute. Our players must give the maximum. We have a lot of work to do. We must work hard to keep winning.”
Wednesday made a slow start to the season, but their new arrivals seem to have settled and the side is starting to gel.
The Owls have been very impressive of late, and the quality that they have in their ranks this season is starting to shine through.
Preston, meanwhile, have struggled since being promoted from League One last term, and are still looking to adapt to life at a higher level.
Simon Grayson's men are sat in 22nd place in the Championship table and they have failed to win any of their last six games, but Carvalhal clearly thinks that the result of Saturday's match is far from a foregone conclusion.