Holland was sacked with the Railwaymen propping up the League One table, but no new appointment is in the pipeline.
Gradi told the club's official website: "There is no imminent appointment following last night's board meeting.
"The board want to get the right man in and placing me in charge on a short-term basis lets us bide some time.
"Those discussions amongst the board members will continue and [chairman] John Bowler will continue to keep everyone informed in due course."