However the U's have lost Dan Gleeson to Luton, while Danny Crow and Brian Saah are yet to agree new terms.
The Cambridge United boss believes he needs five new players, but that could reduce to three if Saah and Crow agree to remain at the Abbey Stadium.
"We need a senior centre-half, senior centre-midfielder and a senior centre-forward, to make sure the core of our team is very strong," Ling said.
"I'd like that centre-half to be Brian Saah and expect to have an answer from him soon.
"We will then need another forward to add competition to Marriott, Wright and the senior centre-forward we'll be bringing in. We also need a left-footed winger to give balance to our squad."
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