Introduction: Monitoring athletes' perceived wellness has become an important component of daily tasks of practitioners, yet the properties of brief wellness questionnaires remain insufficiently examined in specific team sport contexts. The purpose of this study was to describe the internal consistency, between-athlete reliability, and estimates of measurement error for a modified wellness questionnaire during short-term field monitoring and to explore associations with selected external monitoring variables. Methods: Routinely collected data from eighteen elite male water polo players were retrospectively analyzed across 12 repeated measurement occasions, resulting in 216 questionnaire observations. The questionnaire assessed sleep quality, physical and, upper- and lower-body fatigue, mental fatigue, and stress, from which composite recovery and fatigue scores were derived. All items were scored so that higher values indicated a more favorable status. External variables included sleep duration, heart rate variability (HRV), and daily summed session-rating of perceived exertion (s-RPE); additional lagged models examined potential delayed associations with recovery and fatigue. Results: Most wellness indicators demonstrated low between-athlete reliability, particularly sleep quality and recovery-related items, indicating substantial within-athlete variability over time. Internal consistency was acceptable for the recovery composite and good for the fatigue composite. SEM values were 0.61 for recovery and 0.59 for fatigue, with corresponding MDC95 values of 1.69 and 1.64. Within-questionnaire mixed-effects models showed that recovery was associated with the stress score across measurement occasions. Exploratory external-association analyses showed that sleep duration was associated with perceived sleep quality and recovery, while HRV was associated with the stress score. Daily summed s-RPE was not meaningfully associated with concurrent wellness scores, although higher previous day s-RPE was associated with less favorable next-day fatigue. Conclusion: The modified wellness questionnaire showed interpretable internal score patterns and selected exploratory external associations during short-term descriptive monitoring in this specific elite water polo setting. However, the findings do not establish full psychometric validation, responsiveness, or suitability for training prescription decisions.
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