The original fixture was due to be played last month but was prevented from taking place due to the Blues' involvement in the FIFA Club World Cup.
Saints will now travel to Stamford Bridge this month, with ticketing details to follow in the coming days.
However, with the two sides due to meet in the FA Cup at St Mary's this weekend, a potential replay would take precedence and would therefore take place on the same day – Wednesday 16th January.
If that particular visit is classed as a third-round replay, our league game at Stamford Bridge would again be rearranged for later in the season.
Ticketing details will be publicised on saintsfc.co.uk
over the next few days