It happened on the stroke of half-time following a collision with North End goalkeeper Andy Lonergan and he was taken to hospital.
Preston boss Alan Irvine: "Youl has a knee injury which we fear might be quite bad.
"There was a little nudge from their striker (Marlon Harewood) and a collision with Lonners, but those sort of things happen.
"Callum Davidson also felt his hamstring go tight and we had to bring him off too.
"That happened right before they scored the goal and that certainly didn't help us.
"I thought we performed well overall and it was a bit harsh - we got undone by a very good piece of finishing.
"We've seen Kevin Nolan do that on many occasions and he's got the quality to be able to do that."