With head coach Steve Cooper under renewed pressure, Marinakis is exasperated over the delay in recruiting what he believes is a crucial position, following his £95 million transfer spend over the summer.
Forest possessed the second worst record in the Premier League last season for goals scored from set-pieces, while this season they have scored just one goal from a dead-ball situation - Willy Boly’s header in the 3-2 defeat at Manchester United in August.
It is understood Marinakis has been demanding a specialist set-piece coach since the end of last season, but Forest are yet to fill the position despite talks with a number of candidates.
Tottenham’s former set-piece coach, Gianni Vio, who has also worked with the Italy national team, is thought to have been one contender but the move collapsed.
Forest have spoken to another candidate in the last 48 hours but, at this stage, it appears the position will remain vacant.
Set-piece specialists are becoming increasingly prevalent in England’s top division, with Arsenal’s Nicolas Jover, Aston Villa’s Austin MacPhee and Manchester City’s Jack Wilson three highly regarded operators in particular.
Forest smashed their transfer record to sign £30million midfielder Ibrahim Sangare from PSV Eindhoven, while another 12 new players arrived.
It takes Marinakis’s spending over the £250million mark since the club’s return to the Premier League after a 23-year absence.
Cooper still has the backing of a large number of supporters, and has delivered positive results in the past when the tide was seemingly turning.
Last season he appeared close to being dismissed after a 4-0 defeat by Leicester City but signed a new contract and then earned widespread praise for guiding the club to safety.
Forest are currently 14th in the table, eight points above the relegation zone.
Meanwhile, the club confirmed they are working with Nottinghamshire Police after “a minority” of fans allegedly directed homophobic language at Brighton’s players and supporters last Saturday.
In a statement, the club said: “Homophobia, like all other forms of discrimination, has no place in football or society, and anyone engaging in discriminatory behaviour is committing a criminal offence.
“We are actively working with Nottinghamshire Police to identify the individuals involved, and they will be dealt with appropriately.
“We would like to thank all our supporters who reported incidents. Nottingham Forest is committed to creating an inclusive environment which embraces and celebrates our differences. We want everyone who attends our stadium to have a positive experience.”