Cardio isn't needed in a soccer player's program in the form of mileage/long runs.
When it comes to running, soccer players need to develop these things:
Acceleration allows one to accelerate rapidly to the ball, simply known and necessary. Max velocity work allows all around development of speed and neural adaptions to speed.
Now RSA which stands for Repeated Sprint Ability. Soccer players jog jog jog... SPRINT, jog jog jog... SPRINT. RSA is best developed through general use of proper speed work with full recovery, accelerations up to 20m with limited recovery time and tempo.
So speed work should have its place and proper use, now lets move onto developing the RSA. To generally condition a athlete we will use tempo and use two forms: extensive and intensive.
For better conditioning intensive (80%-90%) speed is used over 50-200m distances. This will build up a athlete's all around fitness.
Extensive tempo is used at variety of speeds under 75% to allow for both recovery and development of VO2.
So there we cover a athlete's base conditioning. Now for more specific development of RSA we will use accels with limited recovery time as well as f-s-f/s-f-s. For limited recovery time accels, 10-20m is ideal. Starting off with 1 minute rest between runs and lowering recovery every session is best way to go to allow for best adaption.
S-F-S/F-S-F goes like this. Mark out every 20m through a distance of 60m. What you do is start off jogging for 20m, then sprint for 20m, and jog for 20m. Or do the opposite and sprint for 20m, slow down to a job for 20m, then sprint again. You can do 5 instead of 3 runs.