City and Millwall's ball number 19 were drawn alongside Jose Mourinho's Blues - the current joint leaders of the Premiership - meaning whoever wins next Wednesday's replay will travel to Stamford Bridge towards the end of January.
All fourth round ties will be played over the weekend 24/25 January 2015.
The Bantams' third round replay with Millwall will be held at the Coral Windows Stadium in nine days time following an exciting 3-3 draw at The Den on Saturday.
Complete ticket details for next Wednesday's replay with Millwall will be confirmed in due course.