In an individualized athlete's conditioning program, it is desirable to use techniques of single-case research. However, it remains an unsettled question whether statistical analyses are possible in a single-case design. The purpose of the present study was to evaluate the conditioning of a tennis player by statistical analyses over a season using a single-case design. Two male collegiate tennis players (subjects A and B) were observed independently and monitored by self-monitoring sheets during a 6-month tennis season (off-season, preseason, and in-season) using parameters such as performance readiness and performance. Factor analysis was used to extract the fluctuation components of performance readiness. A randomization test was used to examine the difference between means of performance readiness between Deltaoff-pre, Deltapre-in, and Deltaoff-in seasons. The performance readiness increased significantly (p < 0.05) toward a peak date in subject B (p < 0.05). In conclusion, a randomization test was an effective coaching tool to evaluate the conditioning of a tennis player over a training season.