Ferdinand's contract with Manchester United expires next summer and despite ruling out an immediate offer, Allardyce believes that a deal at the end of this season could be a possibility.
The Hammers manager said: "I think it's highly unlikely that we would consider Rio Ferdinand at the moment.
"But if it's at the end of the season and he hasn't got a new contract and he is going to leave Manchester United then we would be interested if we can sustain our Premier League status. It depends entirely on Rio.
"Everything has to be in place. If Rio wants to come back, the financial package and so on and so forth and whether they want to release him or not."
Ferdinand started his career at Upton Park before joining Leeds United in 2000.