Jose Mourinho has urged the Manchester United hierarchy to make a move in the transfer market or be left behind by their Premier League rivals.
United have been linked with the likes of Harry Maguire and Toby Alderweireld in recent weeks but are yet to add to the arrivals of Fred, Diogo Dalot and backup goalkeeper Lee Grant.
The lack of transfer movement at Old Trafford has come against a backdrop of heavy spending at Liverpool, while champions Manchester City have added Riyad Mahrez to the squad that finished 19 points clear at the top last season.
Speaking before his side's lacklustre 1-0 friendly loss to Bayern Munich in Germany, Mourinho delivered a pointed warning to the figures controlling the purse strings.
"My CEO [Ed Woodward] knows what I want for quite a long time,"Mourinho told MUTV.
"He knows what I want, I know that he tries to do the best for me and I still have a few days to wait [and see] what is going to happen.
"The other clubs that compete with us are really strong and already have fantastic teams and squads, like Chelsea, Tottenham, Manchester City, or they are investing massively like, for example, Liverpool, that is buying everything and everybody.
"So if we don't make our team better it will be a difficult season for us."
United get the Premier League season underway at home to Leicester City on Saturday (AEST).
FIFA World Cup participants Romelu Lukaku, Jesse Lingard, Paul Pogba and Marouane Fellaini all enter the new campaign without an appearance in what has been a troubled pre-season headlined by Mourinho's frustration over player availability.