The New Zealand international has played a key figure in West Ham's promising start to the campaign - helping Allardyce's men to fourth place in the Premier League.
However, Reid is in the final year of his contract at Upton Park and has yet to put pen to paper on a new deal.
Despite the risk of losing the 26-year-old on a free transfer at the end of the season, Allardyce says Reid will not be sold in January unless the club receives a suitably impressive offer.
"He ain't going anywhere," Allardyce told reporters.
"He is not going anywhere unless someone bids £20m or something like that.
"If somebody flirts around with a measly offer because he is in the last year of his contract, we would make more money by keeping him and finishing where we are in the league, rather than selling him and putting our good season in jeopardy.
"Because replacing him in January - replacing anybody in January - is a very difficult job indeed."
