Grayson will finalise his list early next week, once the dust settles on today’s clash with Leeds at Deepdale (12.30pm).
The Lilywhites have eight players out of contract next month, six of them currently away on loan.
Chris Kirkland and Neil Kilkenny are the two who have stayed put at Deepdale to remain in Grayson’s plans.
Kirkland has started the last two games in place of the injured Anders Lindegaard.
Grayson said: “Doing the retained list is a tough part of the job, any manager will say the same thing.
“It was a difficult time a couple of weeks ago, meeting with the scholars about who was going to be kept on.
“When we do the first-team players, it will be tough.
“I have got to know these lads really well and worked with them closely.
“But these are the decisions you have to make as a manager. Last year was difficult as well because we won the final at Wembley and two days later I was releasing players.
“It is part and parcel of the job, you have to keep improving the squad by making decisions which are sometimes ruthless.
“We will be doing the retained list in the early part of next week.”
Josh Brownhill, Kyel Reid, Andy Little, Nick Anderton, Jack Ryan and Josh Heaton are the others approaching the final stages of their contracts.
Grayson is determined to push North End forward next season in what he predicts will be a Championship even tougher than this season.
He said: “We have to be better, if you don’t try and improve, you get found out.
“I have to keep improving as a manager, my staff have to improve and the players need to push on another level.
“When you look at the division for next season, the three teams who come down from the Premier League will make things really tough.
“The teams who just miss out on going up this time will want to go again, then there are the ones who have under-achieved.
“We are doing our work to get the recruitment done and the challenge of next season is one we are looking forward to.
“When you look at what we have done this season, we can be extremely pleased.
“The players have been fantastic to work with, they have given their all in every training session.
“The times when I’ve had to have a go at them, have been few and far between.
“We have achieved what we have done despite having three long-term injuries.
“Jermaine Beckford was out for a long time, Stevie May has missed large parts after we spent a lot of money on him, Chris Humphrey too has been out since October.
“We have not carried a big squad and for the last three or four months, we have often been down to the last 18 or 19 players for games.”