In the latest odd twist in the saga of Miami Beach’s oft-delayed convention center redevelopment, a city commissioner on Wednesday alleged that a project bidder may have had improper “contact’’ for possible bid-rigging with the city’s former procurement director, who is facing unrelated public-corruption charges.

Commissioner Deede Weithorn, who raised the allegation in a commission meeting and in a subsequent public statement, did not name the bidder or specify the nature of the alleged contact. She later acknowledged in a brief interview she has “no proof,’’ but said the allegation came from a trusted, unnamed “source.’’

Weithorn made the claim as she asked fellow commissioners to “reconsider’’ a December vote that narrowed down the field of development teams competing for the massive project to the two groups that scored highest in a city evaluation. Though Weithorn voted with the majority, 6-1, she later said the decision was made with insufficient analysis and wanted consideration of adding a third team.

Though she could not get another commissioner to go along with reopening the decision, Weithorn won agreement to require all five bidders to submit affidavits attesting they had no improper contact with former procurement director Gus Lopez or his “agent.’’ A false affidavit could lead to perjury charges, she noted.

Representatives of the two top-ranked teams, Portman-CMC and South Beach ACE, said they were willing to sign. The city attorney’s office will draft the affidavit.

But Weithorn’s latest sally cast a new shadow over the troubled, years-long effort by the city to renovate its aging convention center, add a hotel and redevelop 26 acres of city land around it with a combination of housing and commercial buildings to be financed mostly privately. The 52-acre project in the middle of South Beach, which the city says could cost anywhere from $500 million to $1 billion, is considered to be among the most significant in the country.

The bidding for the project, launched a year ago after an earlier effort ground to a halt, was suspended again while state investigators looked into the allegations against Lopez and a business associate, Pierre Landrin Jr. The bidding process resumed last fall after prosecutors assured the city that their investigation had yielded no evidence that the convention center bids were tainted “at this time.’’

On Wednesday, a spokesman for the state attorney’s office said he had nothing new to add to that previous statement.

Some bidders and observers raised concerns that Weithorn’s allegations could derail the complex project by giving the deep-pocketed investors necessary for its success cold feet.

Anthony Alfieri, director of the Center for Ethics and Public Service at the University of Miami’s law school, said Weithorn’s vague allegation and the commission’s demand for affidavits also raise some potential issues related to fairness and the integrity of the city’s bidding process. He said the bidders are put in a difficult position by being asked to “prove a negative’’ in denying an allegation whose details they are not privy to.

“The commission has essentially created a cloud over the bidding process and the bidders. They have to prove they did not engage in unethical or unlawful conduct, but without a clear-cut method of doing so. They are at a significant disadvantage in proving their own innocence when they haven’t been accused of clear-cut misconduct,’’ Alfieri said.