The defeat was the first in eight Championship fixtures for Carlos Carvalhal's side.
The Owls fell to their first defeat in eight Championship games when they came up against Simon Grayson's men on Saturday, but Lees has insisted that they have done too much work in recent months to throw in the towel regarding their promotion hopes.
"If you take Saturday away, we are probably the form team in the division. We can't forget that after one game," he told the Star.
"We are not going to think the season is over after one defeat. We have to make sure we start the run again on Tuesday.
"We have lots of reasons to be positive. We are on a good run, we are right in the play-off mix, have a great squad and lots of options."
Despite the loss to the Lilywhites, Carlos Carvalhal's men remain in the play-off places in the division, and have shown plenty in recent weeks to suggest that they will be well in contention for promotion come the end of the season.
Only Burnley and Fulham have scored more goals than Wednesday this term. And while they will be without top scorer Fernando Forestieri for their game against Queens Park Rangers on Tuesday, their opponents have the joint-worst defensive record of any side in the top half of the division, so may well be the perfect side for the Owls to come up against if they hope to restore any belief that was lost at Deepdale on Saturday.