Personally I would have them doing short sharp sprints and turning drills.Try put a green marker and yellow marker 20 yards apart and you stand in the middle.Get them on there toes and call out a colour.They then have to sprint to that colour,sprint back to the other colour then back to the middle.Repeat several times.Get them also doing lofted passes or driving passes.Anything like short passing wont work as there isnt much effort needed.
Hope this helps.
Also ask the player to be truthful.I had a girl yesterday that played unfit and by half time she said she was injured.She didnt tell me it was an injury she already had before the game so it cost me a sub and shes likely to be out longer know for not resting it