Sir Alex Ferguson's apology to Alan Wiley has been described as "half-hearted" by Alan Leighton, the national secretary of the union Prospect that represents match officials.
Ferguson has courted controversy following a personal attack on Wiley that came after a 2-2 draw with Sunderland on October 3. Speaking on ESPN, the Manchester United manager accused the referee of not being fit enough and needing a rest during the game.
It has been reported that Ferguson's criticism forced Wiley to consider his future in the game and the United boss issued an apology after being contacted by the Football Association to explain his contentious comments.
His contrition has not satisfied Prospect though, who have already threatened legal action if the FA does not impose a satisfactory punishment. Instead of drawing a line under the row, they claim Ferguson's apology has broadened the argument by appearing to indicate that the fitness of all referees is a concern.
"I think it's a half-hearted apology at best really, and it probably exacerbates the position, rather than resolving it," Leighton told BBC Radio Five Live.
"He clearly hasn't retracted the statement about Alan being unfit so it's not an apology for the main offence caused - and then he widens it to question the fitness of other referees, so he seems to be opening another can of worms which I don't think is very helpful at all.
"Referees are very fit...they have sports scientists who test them regularly throughout the season. They don't just pass a fitness test at the start of the season. Their body fats and BMI are regularly monitored, there are get-togethers every two or three weeks where they are put through extensive training and testing.
"I think the punishment should be a UEFA-type coaching ban, which is rather more than a touchline ban. Referees always accept decisions are going to be pored over - they have no problem with legitimate criticism.
"What's problematic is when the integrity and key components of refereeing are being questioned in a totally unwarranted and unfounded way - and we will defend our members when they are.''
The passage in Ferguson's apology that appears to have angered Prospect read: "My only intention in speaking publicly, was to highlight what I believe to be a serious and important issue in the game, namely that the fitness levels of referees must match the ever increasing demands of the modern game, which I hope will now be properly addressed through the appropriate formal channels."