As a coach, you should keep track of the presence of your players on practice through the month. I give you here to download an excel file where you simply put in your players, the number of sessions, the number of sessions they attended and the one that they didn’t. The calculation of the average will give you an indication of the attendance in %. If it falls under 70%, something is wrong.
As the report of the head of medicine at Lille (french elite team) says, it is normal that you have, on average, 2 players (squad of 30 players) who cannot practice. If you regularly experience higher numbers than that, you should analyze your work and find objective reasons for that.