In the second half and with the score at 0-0, Forestieri was dismissed for his second bookable offence, with one yellow card coming as a result of a dive and a second caution being received for a deliberate handball.
Seven minutes after he had left the pitch, Preston scored what would turn out to be the winning goal, ensuring that Wednesday failed to extend the gap separating them from the pack of teams chasing a play-off spot.
Despite Forestieri's error in judgement, Lees has backed the attacker to redeemed himself later in the campaign and stressed that everyone associated with the Owls wants to focus on their upcoming fixtures.
Lees said: "These things happen and Fernando is probably more upset than any of us. You win and you lose together, we learn from these things and move on.
“You can see by how Fernando plays, he wears his heart on his sleeve, he is a very emotional player in terms of his desire to win.
"Now we get behind him because it’s important we look after him. He will win us games in the future, we’re fully behind him and want him back on the pitch as soon as we can.”
Since moving to Hillsborough in the summer, Forestieri has scored 12 goals from 26 appearances in the Championship.
The former Watford man will be missing from the club's clash with Queens Park Rangers in midweek, but should return when Wednesday travel to Hull City three days later.