There are no replays in this competition. There will be a winner on the night with extra time and penalties if needed.
Cheltenham Town manager John Ward is looking forward to the clash.
"It's definitely something to get the juices flowing. It's a local derby in the Cup and I'm sure both sets of supporters will generate a terrific atmosphere," Ward said.
"We have a good relationship with Bristol City, I used to be manager there, and I'm sure everyone concerned can't wait for the game."
Gary Johnson will delay naming his team he asses his injury situation.
Louis Carey will be fit to play after receiving stitches in a head wound on the weekend.
"Louis should be okay to face Cheltenham. He had a couple of stitches, but it's nothing serious.
Kick off tonight is at 7:45pm and City fans can pay at the gate at Whaddon Rd.