Christian Purslow says Manchester United will struggle to sign any world class players during the January transfer window.
United have endured a dismal first-half to the season and sit 11 points behind Premier League leaders Arsenal, and the pressure increased on manager David Moyes following Sunday's FA Cup exit to Swansea City.
Former Liverpool managing director Purslow says United possess the financial clout to make waves in the January window but is unsure whether any clubs will be willing to part with key players midway through the season.
Purslow told Transfer Centre: "Manchester United are a club that has more financial resources than any other, and are complying with all the new rules on spending money.
"I think it's remarkable how little they've spent over the years, and that's probably because they haven't had to with the manager they've had.
"It's a new era at United - they've a new chief executive and new manager. It's time for them to start to actually punch at the weight at which they can compete.
"That means buying top class players. But the problem is who can you buy in January? What Champions League club is going to want to strengthen Manchester United when they're a rival?"
Former England midfielder Darren Anderton says United are paying the price for not replacing Paul Scholes last summer.
"The first half of the season has been a real struggle for them," said Anderton. "They're not playing well and the players they brought in last summer, such as Marouane Fellaini, haven't worked.
"They really need a playmaker, someone like Juan Mata. They haven't replaced Paul Scholes and are really struggling."
Sky Sports pundit Tony Gale echoed Anderton's comments and called on Moyes to find a suitable midfield partner for Michael Carrick.
"They needed a central midfielder at the start of the season, someone who could play alongside Carrick," he said.
"Darren Fletcher has just returned after a long illness but you cannot bank on him being the man that'll take United forward.
"They need to bring someone in but it's got to be a quality player, such as Luka Modric, someone who can hold onto the ball in midfield."