Training load is the amount of stress placed on an athlete during a workout session. Competitive tennis players who participate in difficult training and match schedules are vulnerable to injury, emphasizing the importance of training load management. In this study, for seven consecutive months, 26 junior players recorded tennis-related injuries and training load by documenting their length of training and perception of training intensity on a 0-10 scale. Length of training and training intensity were expressed using the acute-to-chronic workload ratio (ACWR), which is the current week’s training load (acute load) divided by the average training load performed in previous weeks (chronic load). The study’s investigators found that if the acute load was more than 1.5 times greater than the chronic load over the previous four weeks, a player was at increased risk of injury. These results suggest that upper-level athletes may be able to use the combination of training length and intensity expressed as ACWR as an initial warning system for injury risk.