Gary Brabin has been in charge of the U's since the summer
Cambridge United boss Gary Brabin says the club must make money available for new signings following their 5-0 FA Trophy mauling at home to Crawley.
Scott Rendell, Lee McEvilly, Danny Brown and Steven Drench have all left the club since the start of the month.
And only midfielder Daryl McMahon has arrived to bolster the U's squad.
Brabin told BBC Radio Cambridgeshire: "If we're going to sustain a serious promotion challenge we definitely need to strengthen."
The defeat to Crawley is Brabin's heaviest since arriving at the Abbey- and it was the U's heaviest since consecutive 5-0 league defeats to Altrincham and York in March 2007.
Last month, the U's board made money available to sign striker Scott Rendell on loan from Peterborough until the end of the season.
But they were forced to pull out of the deal after deciding they could not meet the terms negotiated.
Brabin has used some of the Rendell money to bring in McMahon. But he still says he is operating with one hand tied behind his back.
"Whereas we've lost our two leading scorers for financial reasons, Crawley have gone out and spent money on two players to strengthen their side, who are on more money than any of our players," he said.
"Crawley have gone one way and we need to follow.
"I can't criticise the character of my players, but we're embarrassed by that result."
Leading marksman Lee McEvilly was allowed to leave the club on the understanding Rendell would be staying at the Abbey. And Brabin feels he needs some help from the board in securing a new front-man.
"It was my decision to let Lee McEvilly go because, when we got Scotty that seemed to be a positive move. But we weren't able to finance it and we're now minus a big man."
Meanwhile, academy teenager Sam Ives, 17, made his first team debut against Crawley coming on as a late substitute.
Danny Potter, Wayne Hatswell and Paul Carden are doubts for Saturday's league clash with Woking after being given painkilling injections ahead of the Crawley game.
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