Cambridge chairman Roger Hunt says he is "extremely disappointed" after landlords Bideawhile Limited rejected a £2.2m bid to buy the Abbey Stadium.
Director Dr Johnny Hon had offered to loan the club the money but Bideawhile director and club vice-chairman John Howard rejected it.
"Bideawhile have plans to relocate the club to a community stadium," he told the club website.
"It is not in the club's or company's best interest to start negotiations."
Cambridge fans have reacted angrily to Bideawhile's refusal to sell the Abbey Stadium back to the club.
"This is a kick in the teeth for all our supporters. It puts United's future in the real jeopardy," Cambridge Fans United director Brian Attmore said.
"It is for the whole board to determine what is right for the club and not for one individual with his own commercial agenda," he added.
"This is precisely the conflict of interest we feared would happen."