MANCHESTER, England, Jan 4 (Reuters) - Despite their frustrations, Manchester United fans never booed managers Ole Gunnar Solskjaer or Jose Mourinho - but on Monday Ralf Rangnick heard the full displeasure of the Old Trafford crowd. The German"s decision to substitute Mason Greenwood on the hour provoked loud booing from supporters who had seen the young forward provide the few moments of quality in what had been another dull display from United. It was a vocal criticism of a specific decision, but it also reflected broader concerns that, after improved performances following the dismissal of Solskjaer in November, the quality of United"s displays has been going backwards under the interim manager. That feeling only intensified after Wolves went on to win the game 1-0 for their first victory at Old Trafford in 40 years. In many ways it is an absurd situation -- after all, Rangnick has only been in charge for five league matches and this was his first defeat. But apart from the opening half hour of his debut game against Crystal Palace, there has been little sign of the high-energy, pressing football for which Rangnick was heralded during his time in the Bundesliga. Against Wolves the team looked tactically confused, without any direction and they played with little spirit -- as acknowledged by full-back Luke Shaw after the match. [L1N2TJ1XH} The club had also expected a degree of continuity when they appointed Rangnick with the hope that he could develop the younger coaches that assisted Solskjaer. CONSULTANT ROLE But former player Michael Carrick, who had been caretaker manager, quit on the day the German took charge and then first-team coach Kieran McKenna left to take charge of third-tier Ipswich Town, taking along United colleague Martyn Pert as his assistant. Rangnick, who brought in American former New York Red Bulls coach Chris Armas to assist him, has been placed in charge of the team until the end of this season but he also has a longer-term role as a consultant and will be involved in deciding who the next manager should be. Although he cheekily suggested at his first press conference that he might end up recommending himself, it is his experience as a director of football, creating the right training ground and performance related structures that was the main attraction to the club. The danger is that if Rangnick"s time on the bench sours his relationship with the fans and damages his broader reputation in the game, it may undermine his eventual broader role and the search for his replacement. What the failures of Mourinho and Solskjaer and Rangnick"s early difficulties highlight is that the United squad needs over-hauling, with better and fresher talent brought in and some of the older or sub-standard players moved on. The club"s recruitment though has been heavily criticised for a series of expensive flops and missed opportunities and that area is surely in need of Rangnick"s attention with a smarter and more streamlined approach introduced. The real danger for United is that if the deeper problems with the squad, recruitment and the club"s structure in general, are not resolved then the next manager will simply have to deal with the same issues that have dogged the last three. Will the likes of Paris St Germain"s Mauricio Pochettino and Ajax"s Erik ten Hag, reported to be favourites for the role, want to risk repeating the same frustrations that faced Solskjaer, Mourinho and before him Dutchman Louis van Gaal? After all, what message did it send that a highly-rated young coach like McKenna would choose to leave such a storied club to try his luck in the third tier? The England manager role used to be described as "the impossible job" because the extraordinary expectations could not be met by the objective realities facing a coach. Given the club"s vast resources, making Manchester United a true title contender again, in the face of Manchester City, Liverpool and Chelsea, is not in itself an unachievable task. But it may continue to be frustratingly out of reach, unless the root causes of failure are addressed.