Orient were thumped 3 - 1 on the weekend at Brisbane Rd by newly promoted Doncaster Rovers. Hero for Donny was Leo Fortune West with 2 goals.
Cardiff are favourites for the game which will be settled on the night. The old days of two legged first round games have past and now it's extra time and penalties to determine the winners.
Whoever progresses to round 2 will find out the next opponents on Saturday afternoon when the draw is made live on Sky at 5:30pm. The Premiership clubs that are not in European action enter at this stage with the clubs who are involved in Europe joining in round 3.
Tickets are still available from the ticket office 0845 345 1400 and you will be able to pay on the night but it is more expensive.
Team news will become available as the game approaches but it's expected that the subs from Saturday will get a start and possibly Stuart Fleetwood, who was 17th man at Rotherham, will take some part.