They're natural 400m runners. Great sprint speed and speed endurance but they don't need anything close to the type of endurance of a literal marathon (or 10k, or 5k, or even a 1500m).
It's strange too because you'd figure that "constant" running of soccer players is very similar to what distance runners call a threshold workout but it turns out that they get enough rest between bouts of fast running that they really aren't doing a threshold workout, they're doing a sprint workout.
The upshot is that Bolt's speed and speed endurance translates well to soccer. He'd still need the skills to play the game though.
For a frame of reference, a world class soccer player runs 10-15km in a 90 min match, with 60 minutes of standing/walking, 25 minutes of jogging, with 3km of hard running, which includes over 600m of actual sprinting. Compare to a world class endurance athlete who runs 10k in 27 min, all of it hard (naturally) with the last 400-ish meters as a sprint. There's a video of Galen Rupp doing a 6x1mile (=9.6km total) workout @ 4:30 pace followed by 10x200m sprints. This is a workout he'll complete in under an hour (50 minutes using standard training principles). Rupp's workout is a threshold workout with speedwork at the end. The comparison here is how different it is to the running in a soccer match.
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