Louis van Gaal says he feels an uncomfortable "twitch" in his backside every time Manchester United play 4-4-2.
Van Gaal faced open criticism from United fans for the first time last week when a section of the travelling support at Loftus Road demanded he ditch his 3-5-2 formation and switch to a more expansive 4-4-2 system.
The manager heeded their words and the move paid off as United beat QPR 2-0, but the United manager did not enjoy the victory as much as he would have liked.
Van Gaal accepts results show United are more effective when they line up in a 4-4-2 system, but he is so concerned about his team's vulnerability that he finds it distinctly uncomfortable to watch.
Sir Alex Ferguson famously described the final stages of a close contest as "squeaky bum time" and Van Gaal has now coined his own take on the sensation he feels at similar periods.
"We have won more with 4-4-2 in a diamond, but when you analyse the game then we have twitched our a**** on the bench," the United manager said.
"I have twitched my a** because we were out of balance.
"I told my players I was squeezing my a** but (they said) it was the wrong expression.
"All the matches when we play 4-4-2 like against West Ham United (when 10-man United scraped a 2-1 win) it was always twitching your a** and I don't like it."
Van Gaal finds it far easier to sit and watch his team play in the 3-5-2 system which he used successfully with Holland at the World Cup.
His enthusiasm for three at the back is not shared by several pundits though.
Ex-United stars Gary Neville and Michael Owen joined the fans who were at Loftus Road in criticising the system this week.
Former captain Neville believes United are "too slow" and "predictable" when they play three centre-backs while ex-England striker Owen claimed Van Gaal's men were not functioning properly as a team.
Van Gaal is convinced his players will be able to adapt to the system, but concedes it may take some time.
"They are still not comfortable (with 3-5-2)," Van Gaal said.
"That is very important that they are comfortable.
"I would like them to feel more comfortable.
"But we have to do our preparation in the season so we are doing a lot of things during the matches.
"But we have had a fantastic run of results except Southampton at home.
"Up to now I am pleased and we are going in the right way."
Unsurprisingly, Van Gaal could not care less about the criticism that has come his way of late.
He added: "The discussion about the system is coming so it is ridiculous.
"I have to communicate with my players and observe my players and analyse my players and my team and my opponent and the quality of my opponent and then I have to make a decision with my staff.
"But I cannot hear or listen to what the media are writing or what other people are saying or writing.
"They are never at the training ground and not attending the meetings.
"My staff is attending the meetings and my players so I have to work with them and a board that believes in the manager and these players."
Regardless of how United line-up, they are overwhelming favourites to beat Sky Bet League Two Cambridge and make it through to the fifth round of the FA Cup on Friday.
Given that they are 76 places below United in the league ladder, Cambridge should pose few problems to the 20-time English champions, who have added seven players at a cost of over £150million this year.
But, Van Gaal being the perfectionist he is, has not left anything to chance.
The Dutchman has studied his opponents in great detail and is expecting them to try to use their height to cause a huge shock.
''Cambridge play very direct, with long balls. They have five or six players above 1m 90cm (6ft 3in) so for us it's difficult to defend and that's why you have to prepare yourself very well,'' he said.