Allardyce revealed on Monday that he expected Reid to depart having failed to agree a new contract at Upton Park, with the New Zealand international defender reportedly attracting interest from Arsenal.
Reid is in his fifth season with West Ham, who slapped a £20 million price tag on the former Midtjylland man last month, but is out of contract at the end of the season.
And Allardyce fears a deal may have already been agreed with regard to Reid's future, contrary to transfer regulations.
"You hear rumours. But can we prove it?," he is quoted as saying by BBC Sport.
Under the Bosman ruling, players can negotiate a pre-contract agreement with a different club when they are in the final six months of their existing contract.
"We have had the regulations for a long, long time," Allardyce added. "If you can prove that clubs have broken the rules, then they are in serious trouble aren't they? But you can't prove it these days. You hear rumours, this, that and the other.
"It might have nothing to do with the two clubs directly, it could be between two agents, so how can you relate that to the football clubs? You can't, so it can all get done that way.
"If he is not going to sign a contract here, I would find it highly unlikely if it is not already verbally done.
"You have to accept the way it is and, contrary to whether it breaks the rules or it doesn't, it happens. It is just one of the ways the football world works."
