Six players from Preston, including two out on loan, were arrested on Thursday as part of the British National Crime Agency's (NCA) investigation into spot-fixing in football.
The group were bailed the same day and Grayson chose to select captain John Welsh and defenders David Buchanan and Bailey Wright against Bristol City on Saturday, while the manager claimed Keith Keane was only on the bench for a 'football reason'.
Preston took the lead at Ashton Gate Stadium through Jack King in the 69th minute but had to settle for a draw against Bristol City when Wade Elliott equalised six minutes later for the hosts.
Grayson said the group of Preston players, including Graham Cummins and Ben Davies who are on loan at Rochdale and York City respectively, had denied they have done anything wrong and the 44-year-old manager claimed he has no reason not to believe them.
"First and foremost it was a shock on Thursday with the news and things that followed," Grayson said in his post-match press conference.
"My personal point of view is that the players are innocent until proven guilty.
"I will back them 100 per cent. I spoke to each individual on Friday when they came back into training and spoke to them again on Saturday morning about their mindset and are they ready to play.
"They have assured me 100 per cent that they have no involvement in this, and I will take their word. People will have to prove that they are guilty in this situation.
"The players know that if they are lying through their teeth and they are guilty, then the consequences will follow. But I'm certainly 100 per cent behind these players. I have got a really good group here and it was a huge surprise on Thursday.
"I have backed them today, playing three of them out of the four. All the decisions were for football reason today in picking the team.
"It has not been easy and I will give a lot of credit to those individuals because it hasn't been easy for them. They showed what good professionals they are by being focused on the game. I have got 100 per cent faith that they will be proved innocent."
The six Preston players, plus Barnsley midfielder Stephen Dawson, were arrested as part of the NCA's investigation into spot-fixing over the past two seasons in English football.
Another six players originally arrested in December were again brought in for questioning on Thursday.
That group consisted of Sam Sodje (Portsmouth), Akpo Sodje (Macclesfield Town), their amateur football playing brother Steve, Ian Goodison (Tranmere), DJ Campbell (Blackburn Rovers) and former Oldham forward Cristian Montano.
