United are in need of some strengthening after falling 11 points behind league leaders Arsenal and dropping out of the FA Cup but Purslow suggests they will battle to lure players from other clubs during then January transfer window.
"Manchester United are a club that has more financial resources than any other, and are complying with all the new rules on spending money," Purslow told Transfer Centre.
"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?"
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