Russell Slade believed Craig Noone was fouled in the box during the second half.
"It looks a strong, strong claim for a penalty," he said.
"Even the centre-half who he'd spoken to admitted it was a penalty but we just don't seem to be getting them at the minute.
"I was a little bit disappointed that some of the things we'd worked on, in the first period there was only just glimpses of really.
"It wasn't a great game or spectacle by either side in the first period and not a lot of opportunities, but that was in contrast to the second half.
"Even though mistakes were made, there were opportunities to be taken and we were looking to do that. We pushed forward.
"I thought Noone made a difference coming on at half-time. We took the game to them and we had some wonderful opportunities to get on the scoreboard.
"They put their bodies on the line. They threw everything at it. I think there were three blocks on the bounce at one stage in their box, so credit to them for defending as well."
Preston boss Simon Grayson still has not seen his side win in the league at Deepdale this season.
"I think the one thing you're going to get from this group of players is that they're spirited," he said.
"They're going to work hard, they've got the desire and they've got the hunger.
"Sometimes they are lacking in quality at this level but I'll take this all day long that they'll put their bodies on the line as you saw in second half.
"We have to have a little bit more belief in the players in themselves, that they can express themselves more, take a little bit more care in that final third to try and take a better option and cause the opposition a few more problems.
"It could have gone either way but ultimately I'm pleased we've kept a clean sheet and got a point, which hopefully we can keep building on because there are no easy games in this division."