Purpose: The monitoring of training loads and quantification of physical performance are common practices in youth soccer academies to support coaches in prescribing and programming training for individuals. The interaction between training load and physical performance is unknown during a preseason period in youth soccer players. The current study assessed changes in training load and physical assessments across a 4-week preseason period. The relationship between physical performance and match playing time in youth male soccer players was also investigated. Methods: The training loads of 25 professional youth academy male soccer players were monitored throughout a 4-week preseason period. Assessments of power, agility, speed, and aerobic capacity were undertaken in the first training session. Session ratings of perceived exertion (sRPE) and well-being questionnaires were collected during all training sessions and preseason matches. Playing time during subsequent competitive matches was recorded. Results: T test and 30-m-sprint assessments, conducted on the first day of preseason, were predictors of sRPE throughout preseason (t test χ 2 /df = 2.895, poor adjustment; 30-m sprint χ 2 /df = 1.608, good adjustment). YoYo Test performance was related with changes in perceived fatigue (χ 2 /df = 0.534, very good adjustment). Faster players reported higher values of sRPE, and players with higher aerobic capacity reported higher levels of fatigue across preseason. Well-being, perceived fatigue and soreness, and sRPE decreased across preseason. Greater match durations were related to higher levels of fatigue during preseason (P < .05). Conclusion: The current study highlights the relationship between training load, physical assessments, and playing time. Coaches and practitioners can use physical test data at the start of preseason as an indication of players that report higher sRPE, perceived fatigue, and reduced well-being across preseason, supporting decisions around individualized training prescriptions. Keywords: athlete monitoring, load management, physical assessment, recovery In recent years, there has been an increase in the profile of youth soccer. 1,2 According to recent data derived from 27 European countries, more than half a million under-14-year-old participants compete in soccer. 3 However, given the rapid annual changes in growth and maturation, 4 injury propensity and overreaching in adolescent athletes are higher versus both adults and younger athletes. 5,6 Therefore, an appropriate balance between training, competition, and recovery is required to minimize injury risk and overreaching in youth soccer. 2 Injury susceptibility and overreaching in youth soccer players are also likely attributed to seasonal variations in load, with peaks in injury observed following periods of inactivity or during rapid spikes in training load, 7 such as during a soccer preseason. 7 Accordingly, there is growing concern relating to heightened injury and overreaching due to high training loads across certain periods within a season in youth soccer. 8 Attempts to quantify the accumulated weekly in-season training load under-taken by young soccer players have been made. 9 A separate investigation has also assessed the in-season changes in physical qualities of elite youth soccer players according to maturity status. 10 However, there is a lack of research quantifying training and match loads across a preseason period in youth soccer players. Training loads can be measured through external or internal load, depending on whether measurements are external or internal to the athlete. 11 External loads relate to the objective measurements of physical work (eg, distances, speeds, and number of movements), 12 whereas internal load refers to the stress imposed on the athlete. 11 For example, the quantification of internal training load is commonly assessed among youth soccer players using session ratings of perceived exertion (sRPE), with well-being questionnaires used to assess the response to training loads. 13,14 Significant correlations between physical performance (ie, sprint, total distance , maximum speed, and average speed) and RPE in training sessions have been found in adolescent soccer players examined during 6 weeks of preseason. 15 However, how these relationships change when match play is considered and how external load is linked with internal load and changing perceptions of well-being