Liverpool legend Jamie Carragher feels Manchester United's spending must continue after their club record deal for Chelsea midfielder Juan Mata.
Carragher wrote in the Daily Mail: "Do not think for one moment the £37million paid for Mata will cure all United's ills. To get back to where they were under Ferguson, dominating domestically and constantly posing a threat in Europe, they need another three or four of those transfers.
"United have never been afraid of spending but since the last time they broke their transfer record - for Dimitar Berbatov (£30.75m) in 2008, four months after they won the Champions League in Moscow - their rivals have been bold.
"The Glazers, by contrast, have been complacent and the evidence across Europe stacks up against them - none of the clubs they want to compete with have hesitated when it comes to paying massive fees.
"Real Madrid have gone beyond £80m twice since 2009; last summer Barcelona paid £51m for Neymar; Paris Saint-Germain went higher to get Edinson Cavani, as did Monaco when they landed Radamel Falcao."
