Patrice Evra has passed a medical and is expected to complete his move to West Ham later on Wednesday, Sky Sports News understands.
Evra, 36, arrived at the club's Rush Green training complex on Wednesday morning ahead of signing a deal until the end of the season.
Sky Sports News understands Everton are also interested in the left-back but he is believed to favour a move to London.
Evra, who spent eight years with United in total - including the 2013/14 season alongside current West Ham manager David Moyes - was sacked by Marseille earlier this season and banned by UEFA following an altercation with a supporter.
The former France captain was sent off before Marseille's Europa League defeat against Vitoria on November 2 last year, after lashing out at a supporter who Evra claimed was abusing him.
UEFA charged the 36-year-old under article 15 of their disciplinary regulations, which deals with the misconduct of players, banning him from their club competitions until June 2018.
The ban only relates to UEFA tournaments and does not prevent Evra from playing in any domestic competitions, including the Premier League.
Evra had joined Marseille in January last year, also on a free transfer, signing an 18-month contract after ending a two-and-a-half-year stint at Juventus.
With Manchester United, the defender made 379 appearances and scored three goals in nine seasons in which he won five Premier League titles, the 2008 Champions League, three League Cups, five Community Shields and the FIFA Club World Cup.